isBeforeOrSameAs method
Returns true if this date is before or same as the given date.
Example:
final date1 = DateTime(2024, 2, 24);
final date2 = DateTime(2024, 2, 25);
final isBefore = date1.isBeforeOrSameAs(date2);
// returns: true
Implementation
bool isBeforeOrSameAs(DateTime date) => difference(date).inSeconds <= 0;