plus method
Returns a new LocalTime with the given duration
added.
If the result exceeds 24 hours, it wraps around from midnight.
Example
final t = LocalTime(23, 30);
final next = t.plus(Duration(minutes: 90)); // 01:00
Implementation
LocalTime plus(Duration duration) {
final totalMilliseconds = toMillisecondOfDay() + duration.inMilliseconds;
final normalized = totalMilliseconds % _dayMilliseconds;
return LocalTime.fromMillisecondOfDay(normalized);
}