docs: protected void removeExpiredMeters() {
      int total = 0;
      int expired = 0;
      Iterator<Map.Entry<Id, Meter>> it = meters.entrySet().iterator();
      while (it.hasNext()) {
        ++total;
        Map.Entry<Id, Meter> entry = it.next();
        Meter m = entry.getValue();
        if (m.hasExpired()) {
          ++expired;
          it.remove();
        }
      }
      logger.debug("removed {} expired meters out of {} total", expired, total);
      cleanupCachedState();
    }