CI failure on python 3.11/3.12: test_update_bumps_version_and_updated_at
asserts updated_at > created_at, but ms-precision timestamps collide when
SQLite create + update fire inside the same millisecond on fast runners.
Microsecond precision (6 fractional digits) keeps ISO-8601 valid, TS
Date.parse handles it natively, and no consumer regex-binds to the
3-digit form. Fixes the repository ordering invariant.