FEAT: Remove dependency on fastchat for model conversation templates

[varshini2305]

Replace FastChat’s custom prompt logic with Hugging Face’s apply_chat_template() and tokenizer_config.json.

• Enable use_fast = True in the tokenizer.
• Update _update_ids() in pyrit/auxiliary_attacks/gcg/attack/base/attack_manager.py to call apply_chat_template(), generating model-specific prompts according to the conversation template.

[varshini2305]

@romanlutz