* Implement PruningCheckpointer for efficient checkpoint management and add comprehensive tests
- Introduced `PruningCheckpointer` to manage checkpoint pruning after each `aput()`, ensuring only the latest checkpoints are retained based on a configurable limit.
- Added migration sweep functionality to clean up legacy checkpoints and prevent database bloat.
- Enhanced `get_checkpointer()` to utilize the new `PruningCheckpointer` and trigger migration sweeps when necessary.
- Developed a suite of integration tests for `PruningCheckpointer`, covering various scenarios including pruning behavior, concurrent writes, and retention policies.
- Implemented tests for migration sweep functionality, ensuring proper partitioning and user version management.
- Added diagnostic helper `db_stats` to provide insights into the database state, including thread and checkpoint counts.
* feat(sessions): enhance pruning logic to handle legacy DBs without writes table
* fix(tests): prevent atexit hook leakage in TestMigrationSweep
* feat(tests): enhance TestPruningCheckpointer to validate put+prune serialization
* feat(tests): refactor mock path implementation for get_db_path in test cases
Xi Zhang
50719ef256