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