fix: move subscription.cancel to async dispose, move removeObserver

@@ -256,7 +256,7 @@ class _MobileScannerState extends State<MobileScanner>
 
   StreamSubscription? _subscription;
 
-  Future<void> initController() async {
+  Future<void> initMobileScanner() async {
     // TODO: This will be fixed in another PR
     // If debug mode is enabled, stop the controller first before starting it.
     // If a hot-restart is initiated, the controller won't be stopped, and because
@@ -284,7 +284,10 @@ class _MobileScannerState extends State<MobileScanner>
     }
   }
 
-  Future<void> disposeCamera() async {
+  Future<void> disposeMobileScanner() async {
+    await _subscription?.cancel();
+    WidgetsBinding.instance.removeObserver(this);
+
     if (controller.autoStart) {
       await controller.stop();
     }
@@ -292,7 +295,6 @@ class _MobileScannerState extends State<MobileScanner>
     // Dispose default controller if not provided by user
     if (widget.controller == null) {
       await controller.dispose();
-      WidgetsBinding.instance.removeObserver(this);
     }
   }
 
@@ -300,19 +302,13 @@ class _MobileScannerState extends State<MobileScanner>
   void initState() {
     super.initState();
     controller = widget.controller ?? MobileScannerController();
-    initController();
+    initMobileScanner();
   }
 
   @override
   void dispose() {
-    if (_subscription != null) {
-      _subscription!.cancel();
-      _subscription = null;
-    }
-
-    disposeCamera();
-
     super.dispose();
+    disposeMobileScanner();
   }
 
   @override
@@ -336,7 +332,6 @@ class _MobileScannerState extends State<MobileScanner>
         unawaited(controller.start());
       case AppLifecycleState.inactive:
         unawaited(_subscription?.cancel());
-        _subscription = null;
         unawaited(controller.stop());
     }
   }