Add sync/jetstream locks and publish helpers
Add modules to create and clean up per-user temp lock files on exit
(cleanUpSyncLockOnExit, cleanUpJetstreamLockOnExit).
subscribeToJetstream now checks/creates a JetStream lock file and sync
writes a sync lock and registers cleanup handlers. Export createUser and
subscribeToJetstream for reuse.
Wire createUser/subscribeToJetstream into scrobble flow and add helper
functions to put song, artist and album records (with validation) and a
stub for scrobble records. Update matchTrack types: releaseDate is now a
string, add mbArtists and MusicBrainzArtist type. Remove some unused
imports.