Allow passing multiple events to InitObserver

src/gaemstone.ECS/Observer.cs

@@ -8,8 +8,11 @@ namespace gaemstone.ECS;
 public static class ObserverExtensions
 {
 	public static unsafe EntityRef InitObserver(this EntityRef entity,
-		Entity @event, FilterDesc filter, Action<Iterator> callback)
+		FilterDesc filter, Action<Iterator> callback, params Entity[] events)
 	{
+		if (events.Length == 0) throw new ArgumentException("Must specify at least 1 event", nameof(events));
+		if (events.Length >  8) throw new ArgumentException("Must specify at most 8 events", nameof(events));
+
 		var world = entity.World;
 		using var alloc = TempAllocator.Use();
 		var desc = new ecs_observer_desc_t {
@@ -19,7 +22,9 @@ public static class ObserverExtensions
 			binding_ctx_free = new() { Data = new() { Pointer = &FreeContext } },
 			callback         = new() { Data = new() { Pointer = &Callback } },
 		};
-		desc.events[0] = @event;
+		var span = desc.events;
+		for (var i = 0; i < events.Length; i++)
+			span[i] = events[i];
 		return new(world, new(ecs_observer_init(world, &desc)));
 	}