Introduce OfflineTrack for use with OfflinePlaylist

[semohr]

This pull request introduces the new OfflineTrack class to provide an in-memory representation of tracks, similar to the existing OfflinePlaylist. This allows us to preserve track information even after deletion from the remote service, and to keep the Playlist class hierarchy cleanly separated between in-memory and service-synced implementations.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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[pSpitzner]

Looks good to me.

Im still wondering how this helps with our desired synced-playlists-history class (that serves as ground truth, where we keep track of two remote playlists, and have for each track on each side a time stemp when it was added/moved/deleted)

but thats a topic for a pen-and papter discussion.

[semohr]

Im still wondering how this helps with our desired synced-playlists-history class (that serves as ground truth, where we keep track of two remote playlists, and have for each track on each side a time stemp when it was added/moved/deleted)

I ran into issues with OfflinePlaylist not being truly decoupled from the services. I'm still experimenting with different syncing ideas, but introducing OfflineTrack has resolved several a few headaches for me 😆