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/callback/__init__.py

@@ -437,15 +437,23 @@ class StreamingHandler:
 
     async def _cancel_flush_task(self):
         """
-        取消当前的定时刷新任务
+        停止当前的定时刷新任务。
+
+        停止流式输出时，刷新任务可能已经在线程池里发出了首条消息。
+        这里先等待该轮刷新自然完成，确保 message_id 等返回信息能落回本地状态；
+        否则最终刷新会误以为尚未发送过消息，从而再次发送一条新消息。
         """
-        if self._flush_task and not self._flush_task.done():
-            self._flush_task.cancel()
+        current_task = asyncio.current_task()
+        if (
+            self._flush_task
+            and not self._flush_task.done()
+            and self._flush_task is not current_task
+        ):
             try:
                 await self._flush_task
             except asyncio.CancelledError:
                 pass
-            self._flush_task = None
+        self._flush_task = None
 
     async def _flush(self):
         """