core: In astream_events propagate cancellation reason to inner task (#26727)

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libs/core/langchain_core/tracers/event_stream.py

@@ -994,6 +994,10 @@ async def _astream_events_implementation_v2(
                     del event["data"]["input"]
 
             yield event
+    except asyncio.CancelledError as exc:
+        # Cancel the task if it's still running
+        task.cancel(exc.args[0] if exc.args else None)
+        raise
     finally:
         # Cancel the task if it's still running
         task.cancel()