dispose of controllers in example app

@@ -15,7 +15,7 @@ class _BarcodeListScannerWithControllerState
     with SingleTickerProviderStateMixin {
   BarcodeCapture? barcodeCapture;
 
-  MobileScannerController controller = MobileScannerController(
+  final MobileScannerController controller = MobileScannerController(
     torchEnabled: true,
     // formats: [BarcodeFormat.qrCode]
     // facing: CameraFacing.front,
@@ -174,4 +174,10 @@ class _BarcodeListScannerWithControllerState
       ),
     );
   }
+
+  @override
+  void dispose() {
+    controller.dispose();
+    super.dispose();
+  }
 }

@@ -15,7 +15,7 @@ class _BarcodeScannerWithControllerState
     with SingleTickerProviderStateMixin {
   BarcodeCapture? barcode;
 
-  MobileScannerController controller = MobileScannerController(
+  final MobileScannerController controller = MobileScannerController(
     torchEnabled: true,
     // formats: [BarcodeFormat.qrCode]
     // facing: CameraFacing.front,
@@ -172,4 +172,10 @@ class _BarcodeScannerWithControllerState
       ),
     );
   }
+
+  @override
+  void dispose() {
+    controller.dispose();
+    super.dispose();
+  }
 }

@@ -17,7 +17,7 @@ class _BarcodeScannerReturningImageState
   BarcodeCapture? barcode;
   MobileScannerArguments? arguments;
 
-  MobileScannerController controller = MobileScannerController(
+  final MobileScannerController controller = MobileScannerController(
     torchEnabled: true,
     // formats: [BarcodeFormat.qrCode]
     // facing: CameraFacing.front,
@@ -168,4 +168,10 @@ class _BarcodeScannerReturningImageState
       ),
     );
   }
+
+  @override
+  void dispose() {
+    controller.dispose();
+    super.dispose();
+  }
 }