Finished up MVP for scene callbacks

NuakeNet/src/EngineSubsystem.cs

@@ -20,9 +20,29 @@
         }
 
         public virtual void Initialize() {}
-        public virtual void OnScenePreInit(Scene scene) {}
-        public virtual void OnScenePostInit(Scene scene) {}
-        public virtual void OnSceneUnloaded(Scene scene) {}
+        
+        public virtual void OnScenePreInitialize(Scene scene) {}
+        public virtual void OnSceneReady(Scene scene) {}
+        public virtual void OnScenePreDestroy(Scene scene) {}
+        
         public virtual void OnTick(float deltaTime) {}
+        
+        // Since the engine doesn't have the concept of scene instances, we just pass
+        // a new `Scene` here since all functions in Scene are statics. This is largely
+        // to keep the API a little more stable going forward.
+        private void InternalOnScenePreInitialize()
+        {
+            OnScenePreInitialize(new Scene());
+        }
+        
+        private void InternalOnSceneReady()
+        {
+            OnSceneReady(new Scene());
+        }
+
+        private void InternalOnScenePreDestroy()
+        {
+            OnScenePreDestroy(new Scene());
+        }
     }
 }