fix: Bind CallbackAwaiter during initialization

Author: fuzzybinary

src/dart/godot_dart/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.5.1
+
+- Bind `CallbackAwaiter` during initialization.
+
 ## 0.5.0
 
 - Variant can now be constructed from an Object without using `fromObject`

src/dart/godot_dart/lib/godot_dart.dart

@@ -50,6 +50,7 @@ void _registerGodot(int libraryAddress, int bindingCallbacks) {
   TypeInfo.initTypeMappings();
 
   SignalAwaiter.bind();
+  CallbackAwaiter.bind();
 
   if (Engine.singleton.isEditorHint()) {
     Future.microtask(() async {