message: refactor: add shift, instead of subtracting
  So `that` frame values match the annotation comments in uni tests. Does not influence the algorithm behavior so far.
diff: @@ -20,7 +20,7 @@ class FrameShiftDetector {
  /** Updates detector's state */
  void update(int shift, int pos) {
  oldFrame = frame;
  - frame -= shift;
  + frame += shift;
  frame = wraparound(frame, 3);
  // Whether transitioned from no shift to shift
  