DateTime equality fails

[JCKodel]

Equal DateTimes often returns false because Dart implementation of DateTime is a huge mess (two equal dates are considered different when one is local and the other is UTC, even if they are exactly the same date and time.

DateTimes should be compared exclusively through the millisecondsSinceEpoch, since that is always in UTC, and it doesn't care about precision (most of the time, microseconds are not even considered nor supported).

So, I think the default DateTime equality comparer should be written as this:

import 'package:collection/collection.dart';

final class DateTimeEquality implements Equality<DateTime> {
  const DateTimeEquality();

  @override
  bool equals(DateTime e1, DateTime e2) {
    return e1.millisecondsSinceEpoch == e2.millisecondsSinceEpoch;
  }

  @override
  int hash(DateTime e) {
    return e.millisecondsSinceEpoch;
  }

  @override
  bool isValidKey(Object? o) {
    throw UnimplementedError();
  }
}

And that should be the default (so we don't need to use

@DataField(equality: DateTimeEquality())
final DateTime created;

)

(maybe a build option to not break anything)?