Avoid logging unnecessary stacktraces when shutdown is happening

[BulkBeing]

When a map pod is deleted, it logs below critical errors with stack traces:

2026-03-04 02:45:22 CRITICAL UDFError, re-raising the error
Traceback (most recent call last):
  File "/opt/venv/lib/python3.11/site-packages/pynumaflow/mapstreamer/servicer/async_servicer.py", line 52, in MapFn
    async for msg in global_result_queue.read_iterator():
  File "/opt/venv/lib/python3.11/site-packages/pynumaflow/shared/asynciter.py", line 20, in read_iterator
    item = await self._queue.get()
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/asyncio/queues.py", line 158, in get
    await getter
asyncio.exceptions.CancelledError

<-- above error 3 more times -->

2026-03-04 02:45:22 CRITICAL
[2026-03-04T02:45:22+0000] CRITICAL [] module=server:
[2026-03-04T02:45:22+0000] INFO [] module=server: Killing process: Got exception UDF_EXECUTION_ERROR(udf): CancelledError()
2026-03-04 02:45:22 INFO     Killing process: Got exception UDF_EXECUTION_ERROR(udf): CancelledError()
/app/entry.sh: line 38:     7 Killed                  python -m "$EVENT_DRIVEN_APP_MODULE" "$UDF_NAME"

This is confusing for the user as this is a normal shutdown and there was no UDF exceptions. We need to catch these exceptions.

[kohlisid]

This should get covered with #325 and #323 right? @BulkBeing