feat(metadata): extract metadata from file paths with regex rules (#1669)
Let libraries define ordered regex rules that read title, authors, series,
series number and dates from each book's path relative to its library folder.
Run rules in a bounded worker pool, honour source precedence and field locks,
and apply them on scans, uploads and watcher moves. Also retry unprobed M4B
tag writes with the mp4 muxer.
Closes#1351
Co-authored-by: neon <18559658+neonsolstice@users.noreply.github.com>
Dennis
428aefe8d1