Add musicbrainz_best_album() that resolves an artist+track pair to its
best studio album via the MusicBrainz search API, with a 1 req/sec
courtesy rate-limiter. Prefers plain studio albums over compilations,
singles, and live releases; falls back to any release group when no
studio album is found. Never raises — returns None on any failure.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
