CLI: Fix unsafe arg access of unused args

[Jack-Khuu]

As described in Issue 932, the legacy implementation of the arg parser results in subcommands requiring the existence of cli args that they don't actually use.

This PR fixes this by doing a safe getattr check instead of a raw field access.

As a side effect, it also allows us to remove conditional suppression of args. Instead we can just omit the arg from the parser if they aren't needed.

Also happens to solve a --help bug https://github.com/pytorch/torchchat/issues/976

---

chat

 python torchchat.py chat --help
usage: torchchat chat [-h] [--checkpoint-path CHECKPOINT_PATH] [--compile] [--compile-prefill] [--dtype {fp32,fp16,bf16,float,half,float32,float16,bfloat16,fast,fast16}] [--quantize QUANTIZE] [--device {fast,cpu,cuda,mps}]
                      [--dso-path DSO_PATH | --pte-path PTE_PATH] [--max-new-tokens MAX_NEW_TOKENS] [--top-k TOP_K] [--temperature TEMPERATURE] [--hf-token HF_TOKEN] [--model-directory MODEL_DIRECTORY] [-v] [--seed SEED]
                      [model]

options:
  -h, --help            show this help message and exit
  -v, --verbose         Verbose output
  --seed SEED           Initialize torch seed

Model Specification:
  (REQUIRED) Specify the base model. Args are mutually exclusive.

  model                 Model name for well-known models
  --checkpoint-path CHECKPOINT_PATH
                        Use the specified model checkpoint path

Model Configuration:
  Specify model configurations

  --compile             Whether to compile the model with torch.compile
  --compile-prefill     Whether to compile the prefill. Improves prefill perf, but has higher compile times.
  --dtype {fp32,fp16,bf16,float,half,float32,float16,bfloat16,fast,fast16}
                        Override the dtype of the model (default is the checkpoint dtype). Options: bf16, fp16, fp32, fast16, fast
  --quantize QUANTIZE   Quantization options. pass in as '{"<mode>" : {"<argname1>" : <argval1>, "<argname2>" : <argval2>,...},}' modes are: embedding, linear:int8, linear:int4, linear:a8w4dq, precision.
  --device {fast,cpu,cuda,mps}
                        Hardware device to use. Options: cpu, cuda, mps

Exported Model Path:
  Specify the path of the exported model files to ingest

  --dso-path DSO_PATH   Use the specified AOT Inductor .dso model file
  --pte-path PTE_PATH   Use the specified ExecuTorch .pte model file

Generation:
  Configs for generating output based on provided prompt

  --max-new-tokens MAX_NEW_TOKENS
                        Maximum number of new tokens
  --top-k TOP_K         Top-k for sampling
  --temperature TEMPERATURE
                        Temperature for sampling

Model Downloading:
  Specify args for model downloading (if model is not downloaded)

  --hf-token HF_TOKEN   A HuggingFace API token to use when downloading model artifacts
  --model-directory MODEL_DIRECTORY
                        The directory to store downloaded model artifacts. Default: /home/jackkhuu/.torchchat/model-cache

generate

python torchchat.py generate --help
usage: torchchat generate [-h] [--checkpoint-path CHECKPOINT_PATH] [--compile] [--compile-prefill] [--dtype {fp32,fp16,bf16,float,half,float32,float16,bfloat16,fast,fast16}] [--quantize QUANTIZE] [--device {fast,cpu,cuda,mps}]
                          [--dso-path DSO_PATH | --pte-path PTE_PATH] [--prompt PROMPT] [--num-samples NUM_SAMPLES] [--max-new-tokens MAX_NEW_TOKENS] [--top-k TOP_K] [--temperature TEMPERATURE] [--hf-token HF_TOKEN]
                          [--model-directory MODEL_DIRECTORY] [-v] [--seed SEED]
                          [model]

options:
  -h, --help            show this help message and exit
  -v, --verbose         Verbose output
  --seed SEED           Initialize torch seed

Model Specification:
  (REQUIRED) Specify the base model. Args are mutually exclusive.

  model                 Model name for well-known models
  --checkpoint-path CHECKPOINT_PATH
                        Use the specified model checkpoint path

Model Configuration:
  Specify model configurations

  --compile             Whether to compile the model with torch.compile
  --compile-prefill     Whether to compile the prefill. Improves prefill perf, but has higher compile times.
  --dtype {fp32,fp16,bf16,float,half,float32,float16,bfloat16,fast,fast16}
                        Override the dtype of the model (default is the checkpoint dtype). Options: bf16, fp16, fp32, fast16, fast
  --quantize QUANTIZE   Quantization options. pass in as '{"<mode>" : {"<argname1>" : <argval1>, "<argname2>" : <argval2>,...},}' modes are: embedding, linear:int8, linear:int4, linear:a8w4dq, precision.
  --device {fast,cpu,cuda,mps}
                        Hardware device to use. Options: cpu, cuda, mps

Exported Model Path:
  Specify the path of the exported model files to ingest

  --dso-path DSO_PATH   Use the specified AOT Inductor .dso model file
  --pte-path PTE_PATH   Use the specified ExecuTorch .pte model file

Generation:
  Configs for generating output based on provided prompt

  --prompt PROMPT       Input prompt for manual output generation
  --num-samples NUM_SAMPLES
                        Number of samples
  --max-new-tokens MAX_NEW_TOKENS
                        Maximum number of new tokens
  --top-k TOP_K         Top-k for sampling
  --temperature TEMPERATURE
                        Temperature for sampling

Model Downloading:
  Specify args for model downloading (if model is not downloaded)

  --hf-token HF_TOKEN   A HuggingFace API token to use when downloading model artifacts
  --model-directory MODEL_DIRECTORY
                        The directory to store downloaded model artifacts. Default: /home/jackkhuu/.torchchat/model-cache

export

python torchchat.py export --help
usage: torchchat export [-h] [--checkpoint-path CHECKPOINT_PATH] [--dtype {fp32,fp16,bf16,float,half,float32,float16,bfloat16,fast,fast16}] [--quantize QUANTIZE] [--device {fast,cpu,cuda,mps}]
                        [--output-pte-path OUTPUT_PTE_PATH | --output-dso-path OUTPUT_DSO_PATH] [--hf-token HF_TOKEN] [--model-directory MODEL_DIRECTORY] [-v] [--seed SEED]
                        [model]

options:
  -h, --help            show this help message and exit
  -v, --verbose         Verbose output
  --seed SEED           Initialize torch seed

Model Specification:
  (REQUIRED) Specify the base model. Args are mutually exclusive.

  model                 Model name for well-known models
  --checkpoint-path CHECKPOINT_PATH
                        Use the specified model checkpoint path

Model Configuration:
  Specify model configurations

  --dtype {fp32,fp16,bf16,float,half,float32,float16,bfloat16,fast,fast16}
                        Override the dtype of the model (default is the checkpoint dtype). Options: bf16, fp16, fp32, fast16, fast
  --quantize QUANTIZE   Quantization options. pass in as '{"<mode>" : {"<argname1>" : <argval1>, "<argname2>" : <argval2>,...},}' modes are: embedding, linear:int8, linear:int4, linear:a8w4dq, precision.
  --device {fast,cpu,cuda,mps}
                        Hardware device to use. Options: cpu, cuda, mps

Export Output Path:
  Specify the output path for the exported model files

  --output-pte-path OUTPUT_PTE_PATH
                        Output to the specified ExecuTorch .pte model file
  --output-dso-path OUTPUT_DSO_PATH
                        Output to the specified AOT Inductor .dso model file

Model Downloading:
  Specify args for model downloading (if model is not downloaded)

  --hf-token HF_TOKEN   A HuggingFace API token to use when downloading model artifacts
  --model-directory MODEL_DIRECTORY
                        The directory to store downloaded model artifacts. Default: /home/jackkhuu/.torchchat/model-cache

eval

python torchchat.py eval --help
usage: torchchat eval [-h] [--checkpoint-path CHECKPOINT_PATH] [--compile] [--compile-prefill] [--dtype {fp32,fp16,bf16,float,half,float32,float16,bfloat16,fast,fast16}] [--quantize QUANTIZE] [--device {fast,cpu,cuda,mps}]
                      [--dso-path DSO_PATH | --pte-path PTE_PATH] [--tasks TASKS [TASKS ...]] [--limit LIMIT] [--max-seq-length MAX_SEQ_LENGTH] [--hf-token HF_TOKEN] [--model-directory MODEL_DIRECTORY] [-v] [--seed SEED]
                      [model]

options:
  -h, --help            show this help message and exit
  -v, --verbose         Verbose output
  --seed SEED           Initialize torch seed

Model Specification:
  (REQUIRED) Specify the base model. Args are mutually exclusive.

  model                 Model name for well-known models
  --checkpoint-path CHECKPOINT_PATH
                        Use the specified model checkpoint path

Model Configuration:
  Specify model configurations

  --compile             Whether to compile the model with torch.compile
  --compile-prefill     Whether to compile the prefill. Improves prefill perf, but has higher compile times.
  --dtype {fp32,fp16,bf16,float,half,float32,float16,bfloat16,fast,fast16}
                        Override the dtype of the model (default is the checkpoint dtype). Options: bf16, fp16, fp32, fast16, fast
  --quantize QUANTIZE   Quantization options. pass in as '{"<mode>" : {"<argname1>" : <argval1>, "<argname2>" : <argval2>,...},}' modes are: embedding, linear:int8, linear:int4, linear:a8w4dq, precision.
  --device {fast,cpu,cuda,mps}
                        Hardware device to use. Options: cpu, cuda, mps

Exported Model Path:
  Specify the path of the exported model files to ingest

  --dso-path DSO_PATH   Use the specified AOT Inductor .dso model file
  --pte-path PTE_PATH   Use the specified ExecuTorch .pte model file

Evaluation:
  Configs for evaluating model performance

  --tasks TASKS [TASKS ...]
                        List of lm-eluther tasks to evaluate. Usage: --tasks task1 task2
  --limit LIMIT         Number of samples to evaluate
  --max-seq-length MAX_SEQ_LENGTH
                        Maximum length sequence to evaluate

Model Downloading:
  Specify args for model downloading (if model is not downloaded)

  --hf-token HF_TOKEN   A HuggingFace API token to use when downloading model artifacts
  --model-directory MODEL_DIRECTORY
                        The directory to store downloaded model artifacts. Default: /home/jackkhuu/.torchchat/model-cache