agent: Add tests for thread serialization code (#32383)

This adds some unit tests to ensure that the `update(...)`/migration
path to the latest versions works correctly

Release Notes:

- N/A
afab4b522eBennet Bo Fenner committed on 6/9/2025, 12:20:19 PM· committed by GitHubparent0cb7dd2
4 files changedLine totals unavailable