Fix double-use of TempAllocator with observers

src/gaemstone/ECS/Observer.cs

@@ -21,16 +21,16 @@ public static class ObserverExtensions
 	public static unsafe EntityRef RegisterObserver(this Universe universe,
 		FilterDesc filter, Entity @event, Action<Iterator> callback)
 	{
+		var entity = universe.New((filter.Name != null) ? new(filter.Name) : null).Build();
 		using var alloc = TempAllocator.Lock();
 		var desc = new ecs_observer_desc_t {
 			filter = filter.ToFlecs(alloc),
-			entity = universe.New((filter.Name != null) ? new(filter.Name) : null).Build(),
+			entity = entity,
 			binding_ctx = (void*)CallbackContextHelper.Create((universe, callback)),
 			callback    = new() { Data = new() { Pointer = &SystemExtensions.Callback } },
 		};
 		desc.events[0] = @event;
-		var entity = ecs_observer_init(universe, &desc);
-		return new(universe, new(entity));
+		return new(universe, new(ecs_observer_init(universe, &desc)));
 	}
 
 	public static EntityRef RegisterObserver(this Universe universe,