Disable attrs state management on MappedOperator

[uranusjr]

The custom __getstate__ and __setstate__ implementation from attrs interacts badly with Airflow's DAG serialization and pickling. When a mapped task is deserialized, subclasses are coerced to MappedOperator. But when the instances go through DAG pickling, all attributes defined in the subclasses are dropped by attrs's custom state management.

Since attrs does not do anything too special here (the logic is only important for slots=True), we can use Python's built-in implementation instead.

I locally ran airflow scheduler and this seems to fix the exceptions, but it seems difficult to create a meaningful test for this due to all the components involved. Ideas on test setup are much welcomed.

Fix #23838.

[ashb]

Add something to one of the round trip tests in tests/serialization/test_dag_serialization.py? We've already got test_mapped_operator_serde so maybe we just need to add to that test

[ashb]

Though I am surprised that we hit pickle anywhere in the AIP-45 change, since (from a cursor look at the code) it uses the existing serialized tables, get_dag_by_deserialization etc.

[uranusjr]

It might not be pickling per-se (I still have not found the actual direct cause to the issue), but the same marshalling logic (that uses __setstate__) is reused in a lot of places in Python, including the default __copy__ implementation, so that could be the case.