docs: def _clean(self):
          """Check for inactive workers and remove their references."""
          if self._workers:
              for w in self._workers:
                  if w.is_finished():
                      self._workers.remove(w)
  
          if self._threads:
              for t in self._threads:
                  if t.isFinished():
                      self._threads.remove(t)
          else:
              self._timer.stop()