feat!: implement vsti, along with various refactorings and api changes for it

The RPC and sync library mechanisms were removed for now; they never really worked and contained several obvious bugs. Need to consider if syncs are useful at all during the compose time, or just used during intro.

cmd/sointu-play/main.go

@@ -88,7 +88,7 @@ func main() {
 				return fmt.Errorf("the song could not be parsed as .json (%v) or .yml (%v)", errJSON, errYaml)
 			}
 		}
-		buffer, _, err := sointu.Play(bridge.BridgeService{}, song, !*unreleased) // render the song to calculate its length
+		buffer, err := sointu.Play(bridge.BridgeService{}, song, !*unreleased) // render the song to calculate its length
 		if err != nil {
 			return fmt.Errorf("sointu.Play failed: %v", err)
 		}