Performance: only create the OpenAIRealtimeServerEvent TypeAdapter once (#1548)

For every event a new TypeAdapter is created, which has a significant
performance impact.
<img width="1412" height="1166" alt="image"
src="https://github.com/user-attachments/assets/fc1f9629-9342-4347-b4d5-5e218b73c4e8"
/>
Creating it once and reusing it, makes event handling a lot faster.

Co-authored-by: Michiel De Witte <michiel.dewitte@basalte.be>

Author: michieldwitte

src/agents/realtime/openai_realtime.py

@@ -136,6 +136,7 @@ class _InputAudioBufferTimeoutTriggeredEvent(BaseModel):
     audio_end_ms: int
     item_id: str
 
+
 AllRealtimeServerEvents = Annotated[
     Union[
         OpenAIRealtimeServerEvent,
@@ -144,6 +145,15 @@ class _InputAudioBufferTimeoutTriggeredEvent(BaseModel):
     Field(discriminator="type"),
 ]
 
+ServerEventTypeAdapter: TypeAdapter[AllRealtimeServerEvents] | None = None
+
+
+def get_server_event_type_adapter():
+    global ServerEventTypeAdapter
+    if not ServerEventTypeAdapter:
+        ServerEventTypeAdapter = TypeAdapter(AllRealtimeServerEvents)
+    return ServerEventTypeAdapter
+
 
 class OpenAIRealtimeWebSocketModel(RealtimeModel):
     """A model that uses OpenAI's WebSocket API."""
@@ -159,6 +169,7 @@ def __init__(self) -> None:
         self._tracing_config: RealtimeModelTracingConfig | Literal["auto"] | None = None
         self._playback_tracker: RealtimePlaybackTracker | None = None
         self._created_session: OpenAISessionObject | None = None
+        self._server_event_type_adapter = get_server_event_type_adapter()
 
     async def connect(self, options: RealtimeModelConfig) -> None:
         """Establish a connection to the model and keep it alive."""
@@ -479,9 +490,9 @@ async def _handle_ws_event(self, event: dict[str, Any]):
         try:
             if "previous_item_id" in event and event["previous_item_id"] is None:
                 event["previous_item_id"] = ""  # TODO (rm) remove
-            parsed: AllRealtimeServerEvents = TypeAdapter(
-                AllRealtimeServerEvents
-            ).validate_python(event)
+            parsed: OpenAIRealtimeServerEvent = self._server_event_type_adapter.validate_python(
+                event
+            )
         except pydantic.ValidationError as e:
             logger.error(f"Failed to validate server event: {event}", exc_info=True)
             await self._emit_event(