Python: Ensure we skip sending ErrorResponses to LLMs

If an LLM returns an error response, we save the error content in the entity state. When another request is made, these messages appear to be included in the request context. However, the LLM doesn't appear to accept error content; we may need to ensure it's stripped out for subsequent requests.

[2025-12-19T19:20:35.390Z] Traceback (most recent call last):
[2025-12-19T19:20:35.390Z]   File "/Users/phoff/Source/microsoft/agent-framework/python/packages/core/agent_framework/openai/_chat_client.py", line 76, in _inner_get_response
[2025-12-19T19:20:35.390Z]     await client.chat.completions.create(stream=False, **options_dict), chat_options
[2025-12-19T19:20:35.390Z]   File "/Users/phoff/Source/microsoft/agent-framework/python/.venv/lib/python3.10/site-packages/openai/resources/chat/completions/completions.py", line 2672, in create
[2025-12-19T19:20:35.390Z]     return await self._post(
[2025-12-19T19:20:35.390Z]   File "/Users/phoff/Source/microsoft/agent-framework/python/.venv/lib/python3.10/site-packages/openai/_base_client.py", line 1794, in post
[2025-12-19T19:20:35.390Z]     return await self.request(cast_to, opts, stream=stream, stream_cls=stream_cls)
[2025-12-19T19:20:35.390Z]   File "/Users/phoff/Source/microsoft/agent-framework/python/.venv/lib/python3.10/site-packages/openai/_base_client.py", line 1594, in request
[2025-12-19T19:20:35.390Z]     raise self._make_status_error_from_response(err.response) from None
[2025-12-19T19:20:35.390Z] openai.BadRequestError: Error code: 400 - {'error': {'message': "Invalid value: 'error'. Supported values are: 'text', 'image_url', 'input_audio', 'refusal', 'audio', and 'file'.", 'type': 'invalid_request_error', 'param': 'messages[8].content[0].type', 'code': 'invalid_value'}} 

We do have logic to skip the ErrorContent from the messages to LLM. There might be a bug there I guess -

 # Build messages from conversation history, excluding error responses
            # Error responses are kept in history for tracking but not sent to the agent
            chat_messages: list[ChatMessage] = [
                m.to_chat_message()
                for entry in self.state.data.conversation_history
                if not self._is_error_response(entry)
                for m in entry.messages
            ]