4.0: FinalizerError as an ExceptionGroup #564

This was generated by AI during a pre-4.0 audit of main at 9cd88e7.

Observation

FinalizerError (exceptions/lifecycle.py:6) wraps every finalizer failure in .finalizer_errors, so AsyncFinalizerInSyncCloseError (always wrapped, registries/cache_registry.py:110-120) and user finalizer errors cannot be caught by type. The package requires Python 3.11+, where ExceptionGroup and except* exist. Changing the base class after 4.0 is breaking.

Proposal

Make FinalizerError subclass ExceptionGroup (keep ModernDIError as a base if the MRO allows; otherwise decide). .exceptions replaces .finalizer_errors; is_async stays. Decide whether to keep finalizer_errors as an alias for 4.x or remove it with a migration entry.

Acceptance

• except* AsyncFinalizerInSyncCloseError and except* ValueError (user finalizer error) work, with tests for sync and async close.
• except FinalizerError and except ModernDIError still catch it.
• Docs (lifecycle.md, errors-and-exceptions.md) and migration guide updated.