docs: public Duration toDurationFrom(ReadableInstant startInstant) {
          long startMillis = DateTimeUtils.getInstantMillis(startInstant);
          Chronology chrono = DateTimeUtils.getInstantChronology(startInstant);
          long endMillis = chrono.add(this, startMillis, 1);
          return new Duration(startMillis, endMillis);
      }