Prompt template not honored for LlamaCpp mode provider

[sundaraa-deshaw]

Description

I am using the jupyter ai extension with a custom model provider as per steps in https://jupyter-ai.readthedocs.io/en/latest/users/index.html#custom-model-providers

However the custom prompt template is not being used.

Reproduce

1. Declare a custom ModelProvider like

class LLMProvider(BaseProvider, LlamaCpp):
    id = "llama_provider"
    name = "llama provider"
    model_id_key = "llama_provider"
    models = [
        "codellama-7B-Instruct",
    ]

    def __init__(self, **kwargs):
        super().__init__(
            model_id="desco_llm_provider",
            model_path="/path/to/model",
            temperature=0.2,
            max_tokens=128,
            top_p=0.0,
            verbose=True,  # Verbose is required to pass to the callback manager
            n_ctx=1024,
            top_k=1,
            n_gpu_layers=100,
            streaming=False
        )

    def get_prompt_template(self, format) -> PromptTemplate:
        print("format: {format}")
        if format == "code":
            return PromptTemplate.from_template(
                "{prompt}\n\nProduce output as source code only, "
                "with no text or explanation before or after it. "
                "Produce the output in Markdown format"
            )
        return super().get_prompt_template(format)

2. Install the provider as per the instructions
3. Restart Jupyter Lab and connect to the above model
4. Give a prompt input, e.g. write code to transpose a numpy matrix

Generated prompt:

> Entering new ConversationChain chain...
Prompt after formatting:
You are Jupyternaut, a conversational assistant living in JupyterLab to help users.
You are not a language model, but rather an application built on a foundation model from llama provider called llm_provider.
You are talkative and you provide lots of specific details from the foundation model's context.
You may use Markdown to format your response.
Code blocks must be formatted in Markdown.
Math should be rendered with inline TeX markup, surrounded by $.
If you do not know the answer to a question, answer truthfully by responding that you do not know.
The following is a friendly conversation between you and a human.

Current conversation:
Human: generate code to plot line chart from a dict with keys "date" and "price"
AI:  I can help you with this! Here's the code to plot a line chart from a dictionary with keys "date" and "price":
python
import pandas as pd

# create a dataframe from the dictionary
df = pd.DataFrame(data)

# convert date column to datetime format
df['date'] = pd.to_datetime(df['date']),

# plot line chart using seaborn library
sns.lineplot(x='date', y='price', data=df))

Human: write code to transpose a numpy matrix AI:

## Expected behavior

<!--Describe what you expected to happen-->
Expected prompt to be suffixed with :

"Produce output as source code only, with no text or explanation before or after it. Produce the output in Markdown format

## Context

<!--Complete the following for context, and add any other relevant context-->

- Operating System and version: Fedora Linux 8
- Browser and version: Chrome build 119.0.6045.160
- JupyterLab version: 4.0.9