reviseForPlay method
Implementation
AFTimeState reviseForPlay() {
  final pt = pauseTime;
  if(pt == null) {
    return this;
  }
  final now = DateTime.now();
  final sincePause = now.difference(pt);
  final revisedOffset = simulatedOffset - sincePause;
  return copyWith(
    clearPauseTime: true,
    simulatedOffset: revisedOffset,
    actualNow: now
  );
}