Let a connector's teardown cancellation through too

ConnectorNode.stop cancelled its poll task and then caught CancelledError
around the await — the fourth site of the trap 93e4527 closed elsewhere,
swallowing a cancellation aimed at whoever asked for the teardown. It now
calls the shared Node._cancel_task, which keeps retrieving whatever the
loop raised on its way out, as the old `except (CancelledError, Exception)`
did.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K1moruzue2kTJd3uVisgNk

backend/fluksio/flow/connector.py

@@ -161,11 +161,7 @@ class ConnectorNode(Node):
             return
         self._stop_event.set()
         if self._poll_task is not None:
-            self._poll_task.cancel()
-            try:
-                await self._poll_task
-            except (asyncio.CancelledError, Exception):  # noqa: B014 - shutting down
-                pass
+            await self._cancel_task(self._poll_task)
         self._poll_task = None
         self._stop_event = None
         self._last_published = {}