Move queries and types to respective modules

[snejus]

This PR moves query and type definitions away from library.py to dbcore to improve modularity and organization.

Key Changes:

• Query and Type Relocation:
  • PathQuery and SingletonQuery moved from beets.library to beets.dbcore.query.
  • DateType, PathType (and its variants NullPathType), MusicalKey, and DurationType moved from beets.library to beets.dbcore.types.
  • The BLOB_TYPE definition was moved from beets.library to beets.dbcore.query and then referenced in beets.dbcore.types.
  • The human_seconds_short utility function was moved from beets.ui to beets.util due to circular dependency.
• Test Modernization:
  • The PathQueryTest class in test/test_query.py has been rewritten to use pytest.mark.parametrize for more concise and readable test cases.
• Import Updates: All internal references to these moved classes and functions have been updated across the codebase.

[github-actions[bot]]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[semohr]

Thank you for the PR! I really appreciate it, this will make our lives much easier in the long run!