Json mode

[b10902118]

Currently, the json response for keyword extraction is done by:

LightRAG/lightrag/operate.py

Lines 406 to 407 in 186cd34

	result = await use_model_func(kw_prompt)
	json_text = locate_json_string_body_from_string(result)

But today, most language models already support response in json format. Manual parsing is clumsy and can be unstable.
https://github.com/ollama/ollama-python/blob/dc38fe467585037e02a4bc27a100cf6cb10202ff/ollama/_client.py#L277
https://github.com/openai/openai-python?tab=readme-ov-file#nested-params

If this is desired, I can create a pull request. Thanks.

[LarFii]

Thank you very much! We took this approach because some models do not support JSON responses directly, so we opted for a method that, while clumsy, is more universal. However, we would greatly welcome a pull request to add support for models that do provide JSON responses directly.