feat(py): pass pathlib.Path object directly without.read_text()

[chendaniely]

quality of life improvement where querychat will .read_text() for you on a pathlib.Path object.

Currently failing a ruff/pyright check because of system_prompt_

    # Create the system prompt, or use the override
    system_prompt_ = system_prompt_override or system_prompt(
        data_source_obj,
        data_description_str,
        extra_instructions_str,
    )

    # Default chat function if none provided
    create_chat_callback = create_chat_callback or partial(
        chatlas.ChatOpenAI,
        model="gpt-4.1",
    )

    return QueryChatConfig(
        data_source=data_source_obj,
        system_prompt=system_prompt_, # HERE
        greeting=greeting_str,
        create_chat_callback=create_chat_callback,
    )

Argument of type "str | Path" cannot be assigned to parameter "system_prompt" of type "str" in function "__init__"
  Type "str | Path" is not assignable to type "str"
    "Path" is not assignable to "str"Pyright[reportArgumentType](https://github.com/microsoft/pyright/blob/main/docs/configuration.md#reportArgumentType)

[schloerke]

All currently failing lints are passing in #37. Will wait for that to merge before merging this PR.

[schloerke]

• Merge feat(r+py): Add querychat_system_prompt(prompt_path=) support; Export R's df_to_schema() #37

[schloerke]

Thank you!