Add attribute system with core stats and gameplay components

GameCore/Events/EntitySpawnedEvent.cs

@@ -0,0 +1,11 @@
+using GameCore.ECS;
+using GameCore.Events.Interfaces;
+
+namespace GameCore.Events;
+
+public readonly struct EntitySpawnedEvent(Entity newEntity, Entity owner, string archetypeId) : IEvent
+{
+    public readonly Entity NewEntity = newEntity;
+    public readonly Entity Owner = owner;
+    public readonly string ArchetypeId = archetypeId;
+}