(mobile): ios - calculate hash using CryptoKit (#5976)

* ios: calculate hash using CryptoKit

* chore: remove unused crypto dep

---------

Co-authored-by: shenlong-tanwen <139912620+shalong-tanwen@users.noreply.github.com>
Co-authored-by: Alex Tran <alex.tran1502@gmail.com>

mobile/lib/modules/backup/background_service/background.service.dart

@@ -132,6 +132,7 @@ class BackgroundService {
     }
   }
 
+  // Yet to be implemented
   Future<Uint8List?> digestFile(String path) {
     return _foregroundChannel.invokeMethod<Uint8List>("digestFile", [path]);
   }