music21 api layer for arvo support

[combatopera]

• see https://deepnote.com/@essia/Procedural-music-composition-with-arvo-9b35ebd7-63e0-47bc-a3d5-c503954a083d
• consider using music21 as events implementation, as it seems to do most things well
  • it even has a TinyNotation that could be an alternate lang