Fix dart warnings

finlog_app/fluttery/lib/secure_storage.dart

@@ -60,6 +60,9 @@ abstract class SecureStorage implements Service {
   /// Use with caution as this operation cannot be undone.
   Future<void> deleteAll();
 
+  /// Returns all keys incl. values in secure storage
+  Future<Set<String>> readAll();
+
   /// Returns all keys currently stored in secure storage.
   ///
   /// Useful for debugging or migration purposes.