Apparently, some versionning defines are only present starting at a
specific version...

Use a more robust hack (or uglyness, actually) to wait for discoveries &
FS reloads.
This makes the folders tests green again!

We now only process one file at a time, as we do for snapshots.
The correct way would be to spawn more threads from the Parser class,
shall we want to process multiple items at once

Since the discovery will run in a thread, we can't assume results are
instantly available

failed test > sigsegv

This wrapper is responsible for stacking operations and running them in
a thread, rather than spawning a new std::thread each time

This removes the old std::string artist property on AlbumTrack