MusicBrainz provider refactor and birthday/memoriam/anniversary recommendations

[dmoo500]

Summary

Refactors the MusicBrainz provider into a multi-file package and adds ProviderFeature.RECOMMENDATIONS support.

⚠️ Depends on PR #3811

Refactor: monolithic __init__.py → multi-file package

The existing musicbrainz/__init__.py (~600 lines) is split into focused modules:

File	Purpose
api_client.py	HTTP client with 5 req/s throttling and 30-day caching
models.py	MusicBrainz dataclasses (MusicBrainzArtist, MusicBrainzReleaseGroup, etc.)
constants.py	Shared config key constants (breaks circular-import)
provider.py	MusicbrainzProvider(MetadataProvider) — all existing functionality preserved
recommendations.py	MusicBrainzRecommendationManager — new recommendation logic

Feature: three recommendation types

All three scan the user's library and cross-reference MusicBrainz data:

1. Birthday artists — library artists whose MB life_span.begin date matches today's month/day, grouped by genre into RecommendationFolders with mdi-cake-variant icon.
2. In memoriam artists — library artists whose MB life_span.end date matches today's (only when life_span.ended == True), icon mdi-candle.
3. Album release anniversaries — library albums with a MB release-group ID whose first_release_date matches today, filtered to 5-year milestones only (5, 10, 15, … years ago), icon mdi-calendar-star. Each matching album becomes a playable RecommendationFolder.

Implementation notes

• No wildcard API queries — begin:????-MM-DD returns 0 results on the MA mirror, so the library-scan strategy is used: iterate library items, fetch individual MB records (30-day cached).
• MusicBrainzAPIClient.domain — added domain = "musicbrainz" class attribute required by the @use_cache decorator.
• MusicBrainzReleaseGroup.first_release_date — new optional field populated from the existing release-group/{id} endpoint response.

Tests

17 unit tests covering:

• Birthday date matching (exact, partial/year-only, no life_span, API error)
• In-memoriam date matching + ended=False guard
• _build_artist_folders genre grouping, overrides, and "Other" bucket
• Album anniversary: 5-year match, non-milestone skip, wrong date skip, no MBID skip
• get_recommendations integration for all three types

Note: Depends on #3811. The diff against dev includes commits from that PR; once #3811 merges this PR can be re-based directly onto dev.

[Copilot]

Pull request overview

This PR extends Music Assistant’s cross-type ProviderFeature dispatch so that metadata providers and plugin providers can participate in features like browse/recommendations/similar-* (building on the #3811 groundwork), and updates controllers/base classes plus tests accordingly.

Changes:

• Add MusicAssistant.get_providers_supporting_feature(...) to retrieve providers supporting a feature across provider-type tiers with priority ordering.
• Enable cross-type feature usage in controllers (e.g., browse root and recommendations aggregation; similar-artists endpoint; similar-tracks fallback to metadata/plugins).
• Add/extend base provider APIs (PluginProvider/MetadataProvider) for similar-* and recommendations, update demo plugin provider, and add unit tests.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
music_assistant/mass.py	Adds get_providers_supporting_feature helper and removes plugin-specific feature query helper.
music_assistant/controllers/music.py	Uses cross-type provider lookup for browse root and recommendations; widens provider recommendation typing.
music_assistant/controllers/media/tracks.py	Adds metadata/plugin fallback for similar_tracks.
music_assistant/controllers/media/artists.py	Adds similar_artists API endpoint with music-first, metadata/plugin fallback dispatch.
music_assistant/controllers/media/base.py	Allows get_provider_item to call get_item on plugin providers (in addition to music providers).
music_assistant/models/metadata_provider.py	Adds cross-type feature stubs: similar tracks/artists + recommendations.
music_assistant/models/plugin.py	Adds cross-type feature stubs + playlist/get_item plumbing for plugins.
music_assistant/models/music_provider.py	Adds get_similar_artists abstract method to the MusicProvider base.
music_assistant/providers/_demo_plugin_provider/__init__.py	Documents/illustrates cross-type feature stubs and playlist plumbing for plugins.
music_assistant/providers/qobuz/__init__.py	Removes an unused/empty get_similar_artists stub.
tests/test_cross_type_features.py	Adds unit tests for provider ordering and cross-type dispatch behavior.

[OzGav]

I think the refactor should be one PR and the extra recommendations another. Also there are outstanding PRs which touch the metadata controller and this will mean problems later. I was planning on looking into doing this (so thanks for taking it on) but I was going to wait until all the other changes were merged.

Edit: sorry I misread and this is the musicbrainz controller. Regardless, the PR should only be just that. And my last.fm provider also touches this.

[OzGav]

And why is the Qobuz provider getting touched here?

edit: ok I see this is the result of #3811 . Once that is merged and this is rebased then split this into two.

[dmoo500]

Keeping this as Draft until two upstream PRs are merged:

• Allow Plugin Providers and Metadata providers to implement music related ProviderFeatures #3811 (cross-type ProviderFeature dispatch) — direct dependency
• Add Last.fm Recommendations metadata provider #3020 (Last.fm provider) — adds get_isrcs_for_recording() to musicbrainz/init.py, which needs to be carried over into the refactored api_client.py

Once both are merged, I'll rebase and split this into two PRs:

• MusicBrainz provider refactor (monolithic init.py → multi-file package)
• Birthday/memoriam/anniversary recommendations