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

Autoloads/ConfigFileHandler.cs

@@ -4,13 +4,16 @@ namespace Mr.BrickAdventures.Autoloads;
 
 public partial class ConfigFileHandler : Node
 {
+    public static ConfigFileHandler Instance { get; private set; }
+
     private ConfigFile _settingsConfig = new();
     public const string SettingsPath = "user://settings.ini";
-    
+
     public ConfigFile SettingsConfig => _settingsConfig;
 
     public override void _Ready()
     {
+        Instance = this;
         if (!FileAccess.FileExists(SettingsPath))
         {
             var err = _settingsConfig.Save(SettingsPath);
@@ -24,4 +27,9 @@ public partial class ConfigFileHandler : Node
                 GD.PushError($"Failed to load settings file at {SettingsPath}: {err}");
         }
     }
+
+    public override void _ExitTree()
+    {
+        if (Instance == this) Instance = null;
+    }
 }