advance method
Advances time by seconds
(can be negative to move backwards).
HINT: Useful for simulating window rollovers (±30s).
Implementation
void advance({required int seconds}) {
final next = _epochSeconds + seconds;
if (next < 0) {
throw ArgumentError.value(
seconds,
'seconds',
'Advance would result in negative epoch seconds.',
);
}
_epochSeconds = next;
}