fix: [Litellm]Do not swallow first token (#1316)

`ChatCompletionResponseEventType: start` is ignored and not yielded in
the agent_instance as we expect that to not have any content.

However, litellm sends first event as `ChatCompletionResponseEventType:
start` with content ( which was the first token that we were skipping )

```
LLAMA_STACK_CONFIG=dev pytest -s -v tests/client-sdk/agents/test_agents.py --inference-model "openai/gpt-4o-mini" -k test_agent_simple
``` 
This was failing before ( since the word hello was not in the final
response )

llama_stack/providers/utils/inference/openai_compat.py

@@ -6,7 +6,7 @@
 import json
 import logging
 import warnings
-from typing import AsyncGenerator, Dict, Generator, Iterable, List, Optional, Union
+from typing import AsyncGenerator, Dict, Iterable, List, Optional, Union
 
 from openai import AsyncStream
 from openai.types.chat import (
@@ -841,14 +841,13 @@ async def convert_openai_chat_completion_stream(
     Convert a stream of OpenAI chat completion chunks into a stream
     of ChatCompletionResponseStreamChunk.
     """
-
+    yield ChatCompletionResponseStreamChunk(
-    # generate a stream of ChatCompletionResponseEventType: start -> progress -> progress -> ...
+        event=ChatCompletionResponseEvent(
-    def _event_type_generator() -> Generator[ChatCompletionResponseEventType, None, None]:
+            event_type=ChatCompletionResponseEventType.start,
-        yield ChatCompletionResponseEventType.start
+            delta=TextDelta(text=""),
-        while True:
+        )
-            yield ChatCompletionResponseEventType.progress
+    )
-
+    event_type = ChatCompletionResponseEventType.progress
-    event_type = _event_type_generator()
 
     stop_reason = None
     toolcall_buffer = {}
@@ -868,7 +867,7 @@ async def convert_openai_chat_completion_stream(
             if choice.delta.content:
                 yield ChatCompletionResponseStreamChunk(
                     event=ChatCompletionResponseEvent(
-                        event_type=next(event_type),
+                        event_type=event_type,
                         delta=TextDelta(text=choice.delta.content),
                         logprobs=_convert_openai_logprobs(logprobs),
                     )
@@ -909,7 +908,7 @@ async def convert_openai_chat_completion_stream(
                 toolcall_buffer["content"] += delta
                 yield ChatCompletionResponseStreamChunk(
                     event=ChatCompletionResponseEvent(
-                        event_type=next(event_type),
+                        event_type=event_type,
                         delta=ToolCallDelta(
                             tool_call=delta,
                             parse_status=ToolCallParseStatus.in_progress,
@@ -920,7 +919,7 @@ async def convert_openai_chat_completion_stream(
         else:
             yield ChatCompletionResponseStreamChunk(
                 event=ChatCompletionResponseEvent(
-                    event_type=next(event_type),
+                    event_type=event_type,
                     delta=TextDelta(text=choice.delta.content or ""),
                     logprobs=_convert_openai_logprobs(logprobs),
                 )
@@ -931,7 +930,7 @@ async def convert_openai_chat_completion_stream(
         toolcall_buffer["content"] += delta
         yield ChatCompletionResponseStreamChunk(
             event=ChatCompletionResponseEvent(
-                event_type=next(event_type),
+                event_type=event_type,
                 delta=ToolCallDelta(
                     tool_call=delta,
                     parse_status=ToolCallParseStatus.in_progress,