feat(responses)!: add reasoning and annotation added events (#3793)

Implements missing streaming events from OpenAI Responses API spec: 
 - reasoning text/summary events for o1/o3 models, 
 - refusal events for safety moderation
 - annotation events for citations, 
 - and file search streaming events. 
 
Added optional reasoning_content field to chat completion chunks to
support non-standard provider extensions.

**NOTE:** OpenAI does _not_ fill reasoning_content when users use the
chat_completion APIs. This means there is no way for us to implement
Responses (with reasoning) by using OpenAI chat completions! We'd need
to transparently punt to OpenAI's responses endpoints if we wish to do
that. For others though (vLLM, etc.) we can use it.

## Test Plan

File search streaming test passes:
```
./scripts/integration-tests.sh --stack-config server:ci-tests \
   --suite responses --setup gpt --inference-mode replay --pattern test_response_file_search_streaming_events
```

Need more complex setup and validation for reasoning tests (need a vLLM
powered OSS model maybe gpt-oss which can return reasoning_content). I
will do that in a followup PR.

llama_stack/apis/inference/inference.py

@@ -777,12 +777,14 @@ class OpenAIChoiceDelta(BaseModel):
     :param refusal: (Optional) The refusal of the delta
     :param role: (Optional) The role of the delta
     :param tool_calls: (Optional) The tool calls of the delta
+    :param reasoning_content: (Optional) The reasoning content from the model (non-standard, for o1/o3 models)
     """
 
     content: str | None = None
     refusal: str | None = None
     role: str | None = None
     tool_calls: list[OpenAIChatCompletionToolCall] | None = None
+    reasoning_content: str | None = None
 
 
 @json_schema_type