function epochSecondAndNanoToLocalDateTime (epochSecond, nano) {
  const epochDay = floorDiv(epochSecond, SECONDS_PER_DAY)
  const secondsOfDay = floorMod(epochSecond, SECONDS_PER_DAY)
  const nanoOfDay = secondsOfDay.multiply(NANOS_PER_SECOND).add(nano)

  const localDate = epochDayToDate(epochDay)
  const localTime = nanoOfDayToLocalTime(nanoOfDay)
  return new LocalDateTime(
    localDate.year,
    localDate.month,
    localDate.day,
    localTime.hour,
    localTime.minute,
    localTime.second,
    localTime.nanosecond
  )
}
Converts given epoch second and nanosecond adjustment into a local date time object.
@param {Integer|number|string} epochSecond the epoch second to use.
@param {Integer|number|string} nano the nanosecond to use.
@return {LocalDateTime} the local date time representing given epoch second and nano.