fix: pydantic serializer warning datetime -> int (#1701)

letta/server/rest_api/interface.py

@@ -1001,7 +1001,7 @@ class StreamingServerInterface(AgentChunkStreamingInterface):
                 # Example case that would trigger here:
                 # id='chatcmpl-AKtUvREgRRvgTW6n8ZafiKuV0mxhQ'
                 # choices=[ChunkChoice(finish_reason=None, index=0, delta=MessageDelta(content=None, tool_calls=None, function_call=None), logprobs=None)]
-                # created=datetime.datetime(2024, 10, 21, 20, 40, 57, tzinfo=TzInfo(UTC))
+                # created=1713216662
                 # model='gpt-4o-mini-2024-07-18'
                 # object='chat.completion.chunk'
                 warnings.warn(f"Couldn't find delta in chunk: {chunk}")