The inferred timeline, with adjacent identical chords merged.
The key regions the analysis ran against, in time order. A piece that does
not modulate yields one region covering the whole span; a given key
yields exactly one region too, since the caller has already answered the
question. Either way the first region starts where the analysis does, which
is before beat 0 when the piece opens with a pickup. Pivot chords are filled
in where the chords support one.
The key held longest across ChordTimelineResult.keys — the one to print on a key signature or hand to a generator that takes a single key.
One confidence value in [0, 1] per segment, in segment order.
The result of chordTimelineFromNotes.