Add KION Music (MTS Music) provider (#3100)

* feat(kion_music): add KION Music (MTS Music) provider

Add a new music provider for KION Music (music.mts.ru), the MTS telecom
music streaming service. The provider adapts the Yandex Music API client
(yandex-music library) to work with KION's API endpoint at
music.mts.ru/ya_api.

Features:
- Search (tracks, albums, artists, playlists)
- Library access (liked artists, albums, tracks; user playlists)
- Add/remove library items (like/unlike)
- Streaming with quality selection (High 320kbps / Lossless FLAC)
- Lossless streaming via get-file-info API with flac-mp4 codec support
- Playlist track loading with pagination fix and batch fetching
- Retry on NetworkError to handle transient failures

The provider reuses the same yandex-music==2.2.0 dependency already
present for the Yandex Music provider — no new dependencies required.

Co-authored-by: Cursor <[email protected]>

* chore(kion_music): update documentation URL in manifest

Co-authored-by: Cursor <[email protected]>

* fix(kion_music): fix missing album cover art in library

- In parse_track(), use parse_album() instead of ItemMapping so albums
  get full metadata (including cover_uri) when tracks are synced
- In get_liked_albums(), fetch full album details via client.albums()
  in batches of 50 (likes endpoint returns minimal data without cover_uri)
- Remove unused noqa in provider.py (ruff)

Co-authored-by: Cursor <[email protected]>

* Address PR #3100 review: fix base_url, performance, redundant condition, docstrings; add tests

- Pass KION_BASE_URL to ClientAsync in connect() so API calls go to music.mts.ru
- Use set(batch) for O(1) lookups in get_liked_albums() fallback path
- Remove redundant `track_count > 0` check already guaranteed by outer condition
- Replace "Yandex Music" with "KION Music" in docstrings/comments
- Add full test suite: 5 api_client unit tests, 18 parser tests, 11 integration tests

Co-Authored-By: Claude Opus 4.6 <[email protected]>

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Co-authored-by: Михаил Невский <[email protected]>
Co-authored-by: Cursor <[email protected]>
Co-authored-by: Claude Opus 4.6 <[email protected]>