fix: only initialize once

Chickensoft.AutoInject.Tests/src/auto_node/AutoNode.cs

@@ -22,7 +22,7 @@ void IMixin<IAutoNode>.Handler() { }
   new void Handler() {
     // IAutoOn isn't called since its handler does nothing.
     (this as IAutoConnect).Handler();
-    (this as IAutoInit).Handler();
+    // IDependent invokes IAutoInit, so we don't invoke it directly.
     (this as IProvider).Handler();
     (this as IDependent).Handler();
   }

Chickensoft.AutoInject.Tests/test/fixtures/AutoSetupTestNode.cs

@@ -8,9 +8,18 @@ namespace Chickensoft.AutoInject.Tests.Fixtures;
 public partial class AutoInitTestNode : Node2D {
   public override void _Notification(int what) => this.Notify(what);
 
-  public bool SetupCalled { get; set; }
+  public int Called { get; set; }
 
-  public void Initialize() => SetupCalled = true;
+  public void Initialize() => Called++;
+}
+
+[Meta(typeof(IAutoNode))]
+public partial class AutoInitTestAutoNode : Node2D {
+  public override void _Notification(int what) => this.Notify(what);
+
+  public int Called { get; set; }
+
+  public void Initialize() => Called++;
 }
 
 [Meta(typeof(IAutoInit))]

Chickensoft.AutoInject.Tests/test/src/AutoInitTest.cs

@@ -15,7 +15,7 @@ public void SetsUpNode() {
 
     node._Notification((int)Node.NotificationReady);
 
-    node.SetupCalled.ShouldBeTrue();
+    node.Called.ShouldBe(1);
   }
 
   [Test]
@@ -29,11 +29,22 @@ public void DefaultImplementationDoesNothing() {
   public void IsTestingCreatesStateIfSetFirst() {
     var node = new AutoInitTestNode();
     (node as IAutoInit).IsTesting = true;
+    // Should do nothing on a non-ready notification
+    node._Notification((int)Node.NotificationEnterTree);
   }
 
   [Test]
   public void HandlerDoesNotWorkIfNotGodotNode() => Should.NotThrow(() => {
     var node = new NotAGodotNode();
     (node as IAutoInit).Handler();
   });
+
+  [Test]
+  public void AutoNodeMixinOnlyCallsInitializeOnce() {
+    var node = new AutoInitTestAutoNode();
+
+    node._Notification((int)Node.NotificationReady);
+
+    node.Called.ShouldBe(1);
+  }
 }