Handle UnpicklingError during worker shutdown

[pmontepagano]

When SIGTERM arrives during a _sync_states() call, Python's signal handler interrupts the blocking read() on the multiprocessing proxy connection. The shutdown handler then accesses the same connection (via set_state()), and _ForkingPickler.loads() sees corrupt bytes from the interrupted read, raising _pickle.UnpicklingError.

This adds UnpicklingError to the existing exception handling in:

• WorkerProcess.terminate() — alongside BrokenPipeError, ConnectionResetError, EOFError
• WorkerProcess.exit() — same tuple, for cleanup consistency
• WorkerManager._sync_states() — alongside KeyError

These follow the same pattern already used for other connection-related exceptions during shutdown.

Related: https://community.sanicframework.org/t/random-exceptions-with-workermanager/1154

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.845%. Comparing base (785d77f) to head (9c23ff7).

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #3145       +/-   ##
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+ Coverage   87.793%   87.845%   +0.052%     
=============================================
  Files          105       105               
  Lines         8143      8145        +2     
  Branches      1290      1290               
=============================================
+ Hits          7149      7155        +6     
+ Misses         687       685        -2     
+ Partials       307       305        -2     

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[themavik]

Treating pickle.UnpicklingError like KeyError in _sync_states matches a broken multiprocessing proxy during shutdown. nit: pickle is only imported for the exception type—a short note beside nosec keeps bandit from looking for loads().