Three changes to reduce subsequent index build times:
1. Positive image/rels cache TTL: 30 days → 365 days
Artist url-rels and resolved image URLs rarely change.
Already-indexed artists make zero API calls on rebuild.
2. Negative cache (misses) stays at 30 days so new images
are discovered within a month of being added upstream.
3. MB rate limiter for background indexing: 1.0 → 1.5 req/s
url-rels lookups are lightweight; 1.5/s is well within
what MB handles (Picard and Kodi both use similar rates).
Cuts the MB-bound portion of index build by ~33%.
Also adds NewRateLimiterF for fractional rates and caches
MB rels fetch failures (30-day miss TTL) to avoid retrying
unreachable artists every build.
yonlu
5bb1c89fba