feat: options and ChatCompletionRequest add property enable_thinking

[xuanmiss]

related issue: #2941

enable_thinking is used to control whether the Qwen3 model enables the thinking mode.

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[markpollack]

I'm not sure what to do with these differences emerging, in particular in the reasoning models. This option is not part of openai.

Maybe we can have a subclass of OpenAiChatOptions such as QwenAiChatOptions?

[apappascs]

How about utilizing something like the template pattern? Apart from the openai compatible apis, in general, most of the models just have a few differences on request and response objects

[apappascs]

Thank you for the contribution @xuanmiss . Could you please add some integration tests ?

Given the documentation it's not so clear that this is the correct structure https://qwen.readthedocs.io/en/latest/deployment/vllm.html#thinking-non-thinking-modes.

curl http://localhost:8000/v1/chat/completions -H "Content-Type: application/json" -d '{
  "model": "Qwen/Qwen3-8B",
  "messages": [
    {"role": "user", "content": "Give me a short introduction to large language models."}
  ],
  "temperature": 0.7,
  "top_p": 0.8,
  "top_k": 20,
  "max_tokens": 8192,
  "presence_penalty": 1.5,
  "chat_template_kwargs": {"enable_thinking": false}
}'

As a temporary solution, you can add /think in the end of your prompt.