docs: private static boolean durationIsValid(long seconds, int nanos) {
      if (seconds < DURATION_SECONDS_MIN || seconds > DURATION_SECONDS_MAX) {
        return false;
      }
      if (nanos < -999999999L || nanos >= NANOS_PER_SECOND) {
        return false;
      }
      if (seconds < 0 || nanos < 0) {
        if (seconds > 0 || nanos > 0) {
          return false;
        }
      }
      return true;
    }