A first pass over an unanalysed library is hours of librosa, and there was no
reason for a desktop to spend them one core at a time. Analysis now runs in a
process pool sized by `general.library.analysis_workers`, defaulting to one per
core bar one (capped at 8) when the key is absent.
Two consequences worth knowing before touching this: whatever an `Analyzer`
returns has to be picklable, and an analyzer that keeps state on its own
instance - a test double counting calls - only behaves as written with
`analysis_workers=1`.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
