refactor(dependencies): remove unnecessary 'async' keyword

Remove 'async' from the 'init' method in AppDependencies class.
The method no longer contains 'await' calls, making the 'async'
keyword redundant. This change slightly optimizes the method
definition without altering its functionality.

Author: fulleni

lib/src/config/app_dependencies.dart

@@ -81,7 +81,7 @@ class AppDependencies {
   /// Initializes all application dependencies.
   ///
   /// This method is idempotent; it will only run the initialization logic once.
-  Future<void> init() async {
+  Future<void> init() {
     // If _initCompleter is not null, it means initialization is either in
     // progress or has already completed. Return its future to allow callers
     // to await the single, shared initialization process.