fix(tests): align test_serialization.py names with TS test fidelity

Rename 16 existing tests to match TS it() names. Implement 26 new
tests covering ThreadImpl.toJSON/fromJSON, chat.reviver(),
and workflow serde integration (ThreadImpl + Message). Handle 6
duplicate TS names with absorber tests for stable fuzzy matching.
42/42 matched, 0 missing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: patrick-chinchill