add method
Returns a copy of this with the duration
added, wrapping around midnight.
OffsetTime(Offset(8), 12).add(Duration(hours: -1)); // 11:00+08:00
OffsetTime(Offset(8), 20).add(Duration(hours: 8)); // 04:00+08:00
Implementation
@useResult OffsetTime add(Duration duration) => OffsetTime._(offset, _native.add(duration));