These functions now accept both an ID and data_source parameter,
enabling plugins like mbsync and missing to retrieve metadata from the
correct source.
Update mbsync and missing plugins to use the restored functions with
explicit data_source parameters. Add data_source validation to prevent
lookups when the source is not specified.
Add get_metadata_source helper function to retrieve plugins by their
data_source name, cached for performance.
Move search orchestration into SearchApiMetadataSourcePlugin.
Migrate Deezer, Spotify, and Discogs to provider hooks.
Keep query handling, logging, and limits centralized.
