fix: ensure stop_streaming waits for inflight initial flush before final edit; improve message edit/delete return types and logging

- Update stop_streaming logic to await inflight initial flush task, preventing duplicate message sends on stream stop
- Change message edit/delete methods to return Optional[bool] for clearer channel mismatch handling
- Refine Feishu logging to include message_id instead of full data object
- Suppress allowed_objects warnings in __init__.py
- Add test to verify stop_streaming waits for inflight flush before final edit
- Update .pylintrc to use 'E' for error enabling

app/agent/__init__.py

@@ -16,6 +16,10 @@ from langchain_core.messages import (  # noqa: F401
     HumanMessage,
     BaseMessage,
 )
+
+import warnings
+warnings.filterwarnings("ignore", message=".*allowed_objects.*")
+
 from langgraph.checkpoint.memory import InMemorySaver
 
 from app.agent.callback import StreamingHandler