Add tests for clock_pack_loader edge cases and validation

[Orinks]

Summary

The clock_pack_loader module is at 82% coverage. Several edge cases and error paths are untested:

Uncovered areas (lines 79-80, 84, 95-98, 120, 125-126, 164, 180, 189-190):

1. discover_packs when directory doesn't exist (line 79-80)
2. discover_packs skipping non-directory items (line 84)
3. discover_packs handling ClockPackError and generic Exception during pack loading (lines 95-98)
4. load_pack with invalid JSON manifest (line 120)
5. load_pack with missing required fields (lines 125-126)
6. validate_pack with unsupported audio format (line 164)
7. get_pack returning None for missing pack (line 180)
8. refresh method clearing cache and re-discovering (lines 189-190)

Labels

enhancement, tests

[Orinks]

Completed via PRs #13 and #14 which added 9 edge case tests covering all untested lines in clock_pack_loader.py.