bugfix: handle missing items in Playlist and PlaylistTracks

[Belov-Dev]

Problem:
Spotify API returns simplified playlist objects (e.g. in user playlist lists) where tracks contains only href and total without items.

This causes KeyError/deserialization failure:
Field "items" of type PlaylistTracks is missing in Playlist instance.

Fix:

• Make Playlist.items optional (None default)
• Use d.get("items") or [] in PlaylistTracks.pre_deserialize to handle missing field gracefully

[github-actions]

There hasn't been any activity on this pull request recently. This pull request has been automatically marked as stale because of that and will be closed if no further activity occurs within 7 days. Thank you for your contributions.

[joostlek]

I am not sure when this happens. Can you elaborate what kind of playlists have this and can we add tests for this?

[Belov-Dev]

I am not sure when this happens. Can you elaborate what kind of playlists have this and can we add tests for this?
Unfortunately I can't rollback my local environment, I changed this Spotify plugin to Music Assistant (it has own Spotify integration plugin).