Closes the gap where LockCachingAudioSource wrote files to disk but
never told AudioCacheManager about them — meaning evict() couldn't
reclaim stream-cached files when usage exceeded the cap, only
explicitly-pinned downloads.
Wire just_audio's bufferedPositionStream as the "download complete"
signal: when bufferedPosition reaches duration (with 200ms slack for
header bytes), look up the on-disk file at the LockCaching path,
read its size, and insert an audio_cache_index row via the new
AudioCacheManager.registerStreamCache(). Source defaults to
incidental so stream-cached tracks are first to be evicted under
pressure.
Dedupe via _streamCacheRegistered Set so we don't hit drift on every
~200ms buffered-position emit. Cache the application cache dir path
on first use for the same reason.
Eviction now sees the full set of files on disk; usageBytes() (which
already walks the dir) and evict() (which reads the index) are
finally consistent for stream-cached tracks. Pinned tracks keep
their existing manual-download flow unchanged.
bvandeusen
9cac664679