Add `reasoning_content` to ChatCompletions

[xsoutline]

openai-agents-python/src/agents/models/openai_chatcompletions.py

Lines 210 to 213 in 01f5e86

	delta = chunk.choices[0].delta
	# Handle text
	if delta.content:

在以上代码的位置需要添加处理reasoning_content的流式响应信息事件,或者添加能够添加自定义事件处理程序
示例：

                delta = chunk.choices[0].delta

                # 尝试获取 reasoning_content（模型思考部分），防止属性不存在使用 getattr
                reasoning = getattr(delta, "reasoning_content", None)
                if reasoning:
                    print(reasoning, end='', flush=True)

                # Handle text
                if delta.content:

[weixiewen]

While...delta is from ChoiceDelta, which is from openai types chat...

[Ddper]

Hi @rm-openai I create a PR to solve this issue.
If using reasoning model, it will yield reasoning_content before yield content. It'll yield a title before yield the real content so the user can split the content and reasoning content. Another way is add a <think></think> tag.
Need your opinion.