fix: ensure raw_stream.response is httpx.Response in langfuse streaming adapter

[recursingfeynman]

When Langfuse is enabled, the object passed to OpenAI’s stream manager as raw_stream is adapter LangfuseResponseGeneratorAsync. The OpenAI manager sets self._response = raw_stream.response and then calls await self._response.aclose(). LangfuseResponseGeneratorAsync previously set response to the AsyncStream itself (not to httpx.Response), so the manager tried to call aclose() on an AsyncStream, causing:

AttributeError: 'AsyncStream' object has no attribute 'aclose'

Steps to reproduce

• openai == 2.4.0
• langfuse == 3.7.0

from langfuse.openai import AsyncOpenAI

request_options = {
    "model": "...",
    "messages": [{"role": "user", "content": "Hello"}],
    "n": 1,
}

async with AsyncOpenAI().chat.completions.stream(**request_options) as stream:
    async for event in stream:
        print(event)

---

[!IMPORTANT] Ensure raw_stream.response is httpx.Response by renaming response to stream and setting self.response to stream.response in relevant classes and functions.

• Behavior:
  • Ensure raw_stream.response is httpx.Response in async adapter by renaming response to stream in _wrap and _wrap_async functions.
  • Set self.response to stream.response in LangfuseResponseGeneratorSync and LangfuseResponseGeneratorAsync classes.
• Classes:
  • LangfuseResponseGeneratorSync: Renamed response to stream and set self.response to stream.response.
  • LangfuseResponseGeneratorAsync: Renamed response to stream and set self.response to stream.response.
• Functions:
  • _wrap: Renamed response to stream.
  • _wrap_async: Renamed response to stream.

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[recursingfeynman]

@hassiebp Hi! Maybe add some tests?