Add scene-local CoroutineManager feature

src/CoroutineManager.cs

@@ -8,6 +8,7 @@ namespace HCoroutines;
 public partial class CoroutineManager : Node
 {
     public static CoroutineManager Instance { get; private set; }
+    private static CoroutineManager globalInstance;
 
     public float DeltaTime { get; private set; }
     public double DeltaTimeDouble { get; private set; }
@@ -21,6 +22,34 @@ public partial class CoroutineManager : Node
     private DeferredHashSet<CoroutineBase> activePhysicsProcessCoroutines = new();
     private HashSet<CoroutineBase> aliveRootCoroutines = new();
 
+    public override void _EnterTree()
+    {
+        Instance = this;
+        ProcessMode = ProcessModeEnum.Always;
+        IsPaused = GetTree().Paused;
+
+        if (IsAutoloaded())
+        {
+            // This instance is the global (autoloaded) instance that is shared between scenes.
+            globalInstance = this;
+        }
+    }
+
+    public override void _ExitTree()
+    {
+        if (Instance == this)
+        {
+            // Switch back to the global (autoloaded) manager when the scene-local instance is removed (e.g. when
+            // the current scene is changed).
+            Instance = globalInstance;
+        }
+    }
+
+    private bool IsAutoloaded()
+    {
+        return GetParent() == GetTree().Root && GetTree().CurrentScene != this;
+    }
+
     /// <summary>
     /// Starts and initializes the given coroutine.
     /// </summary>
@@ -56,13 +85,6 @@ private DeferredHashSet<CoroutineBase> GetUpdatePoolOfCoroutine(CoroutineBase co
         };
     }
 
-    public override void _EnterTree()
-    {
-        Instance = this;
-        ProcessMode = ProcessModeEnum.Always;
-        IsPaused = GetTree().Paused;
-    }
-
     public override void _Process(double delta)
     {
         DeltaTime = (float)delta;