despawn method
Removes entity and all of its components. Returns true if the entity
was alive.
Any component value that mixes ServiceMixin has its dispose() fired
(fire-and-forget) so attached subscriptions / timers don't leak.
Implementation
bool despawn(WorldEntity entity) {
if (!_isAlive(entity)) return false;
_cascadeDisposeGroup(entity);
registry.removeGroup(groupEntity: entity);
return true;
}