expiryOf method
Seconds remaining until (entity, type) is removed, or null when
untracked, canceled, or the entity is no longer alive.
Implementation
double? expiryOf(Entity entity, Type type) {
if (!world.isAlive(entity)) return null;
final row = _rowOf(entity, type);
if (row < 0) return null;
final remaining = _deadlines[row];
return remaining < 0 ? 0 : remaining;
}