isExpiredWith method
Returns true if the timestamp plus a given grace duration
has already passed.
Useful for applying a buffer time or tolerance.
If the integer is null, this returns true by default.
Implementation
bool isExpiredWith({Duration grace = Duration.zero}) {
if (this == null) return true;
final inDateTime = DateTime.fromMillisecondsSinceEpoch(this!);
return inDateTime.add(grace).isBefore(DateTime.now());
}