Add event publishing for inventory and combat interactions

GameCore/Events/InstantItemUsedEvent.cs

@@ -0,0 +1,10 @@
+using GameCore.ECS;
+using GameCore.Events.Interfaces;
+
+namespace GameCore.Events;
+
+public readonly struct InstantItemUsedEvent(Entity picker, string itemId) : IEvent
+{
+    public readonly Entity Picker = picker;
+    public readonly string ItemId = itemId;
+}