- Fix RuntimeError: OrderedDict mutated during iteration in SpaceTimeDict
- Fix memory usage and spillover for proper sqrt_n compliance
- Fix thread synchronization with proper locking (cross-platform)
- Fix FileNotFoundError by ensuring directories are created
- Add external_sort_key to exports
- Adjust memory thresholds and test expectations
- Add comprehensive .gitignore file
- Clean up Python cache files
All 14 tests now passing.
