Add tests for uncovered config error/deletion paths

[derek73]

What

Adds three regression tests to tests/test_constants.py covering the last untested behavioral paths in nameparser/config/__init__.py, raising its line coverage from 95% → 97%.

Test	Covers
test_tuplemanager_delattr_removes_dict_entry	del tm.key — the non-dunder branch of TupleManager.__delattr__
test_assigning_non_setmanager_to_cached_union_member_raises	_CachedUnionMember.__set__ TypeError guard when a bare list is assigned to titles/prefixes/etc. instead of a SetManager
test_setstate_raises_on_missing_descriptor_field	Constants.__setstate__ ValueError guard when a pickle blob is missing a descriptor-backed collection

Why

These were the only remaining uncovered lines that represent real behavior rather than reprs. The two error-path tests assert on the exception message content (via pytest.raises(..., match=...)), not just the type — those messages exist specifically to make failures diagnosable, so a message regression would otherwise slip through.

The remaining uncovered lines in the module are two __repr__ methods, a __call__, and a version-conditional typing_extensions import — none worth a test.

Notes for reviewer

• Test-only change; no production code touched.
• Uses pytest.raises for the two error assertions (the base class has no assertRaises shim, and adding one for two call sites wasn't worth ~40 lines of exception-handling machinery).
• Full suite green: 1310 passed, 22 xfailed; ruff clean.

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