Update copyright field type to interface{} in search and tracks OpenA…

[LeonardoSola]

Description

While syncing tracks, the application fails to match some Spotify tracks with Tidal due to a JSON unmarshal error:

2:27AM ERR failed to find track on Tidal error="json: cannot unmarshal object into Go struct field TracksAttributes.data.attributes.copyright of type string" spotify_track_id=56sk7jBpZV0CD31G9hEU3b spotify_track_isrc=USJI10600117 spotify_track_name="Animal I Have Become"
2:27AM ERR failed to find track on Tidal error="json: cannot unmarshal object into Go struct field TracksAttributes.data.attributes.copyright of type string" spotify_track_id=3K4HG9evC7dg3N0R9cYqk4 spotify_track_isrc=USWB10002399 spotify_track_name="One Step Closer"
2:27AM ERR failed to find track on Tidal error="json: cannot unmarshal object into Go struct field TracksAttributes.data.attributes.copyright of type string" spotify_track_id=6RJdYpFQwLyNfDc5FbjkgV spotify_track_isrc=USRE10500766 spotify_track_name=Stricken
2:27AM ERR failed to find track on Tidal error="json: cannot unmarshal object into Go struct field TracksAttributes.data.attributes.copyright of type string" spotify_track_id=0jY829pCMnstlNtaE72vSB spotify_track_isrc=USRE10501019 spotify_track_name=Decadence

This happens because the copyright field returned by Tidal is not always a string — in some cases, it is an object.

Fix

This PR updates the Copyright field type from *string to interface{} to allow proper unmarshalling regardless of the response format.

Notes

The copyright field is currently not used anywhere in the codebase.

This change only prevents the unmarshal error and does not affect existing behavior.

[Zibbp]

Thanks!
FYI I switched over to using https://github.com/spotify2tidal/spotify_to_tidal