compact method
Compact the queue to remove any slots that are no longer used.
The queue, using capacity slots, is reduced to length slots.
Implementation
void compact() {
if (_length == 0) {
_ids = Uint32List(0);
_priorities = Float32List(0);
} else {
_ids = _ids.sublist(0, _length);
_priorities = _priorities.sublist(0, _length);
}
}