refactor: implement singleton pattern for key managers and improve resource access

scripts/Events/SpeedRunEventHandler.cs

@@ -1,5 +1,4 @@
 using Godot;
-using Mr.BrickAdventures;
 using Mr.BrickAdventures.Autoloads;
 
 namespace Mr.BrickAdventures.scripts.Events;
@@ -7,17 +6,18 @@ namespace Mr.BrickAdventures.scripts.Events;
 [GlobalClass]
 public partial class SpeedRunEventHandler : Node
 {
-    private SpeedRunManager _speedRunManager;
-
     public override void _Ready()
     {
-        _speedRunManager = GetNode<SpeedRunManager>(Constants.SpeedRunManagerPath);
-
         EventBus.Instance.LevelCompleted += OnLevelCompleted;
     }
 
+    public override void _ExitTree()
+    {
+        EventBus.Instance.LevelCompleted -= OnLevelCompleted;
+    }
+
     private void OnLevelCompleted(int levelIndex, Node currentScene, double completionTime)
     {
-        _speedRunManager.Split();
+        SpeedRunManager.Instance?.Split();
     }
 }