fix: syntax error in downloads_provider.dart

Fixed duplicated code that caused compilation error:
- Removed duplicate _setError method definition
- Fixed parameter list: void _setError(String? error, [String? stackTrace])
- File now compiles correctly

Error was:
lib/presentation/providers/downloads_provider.dart:173:2: Error: Expected a declaration, but got '?'.
}? error) {
 ^

Fixed by properly replacing the old method with new signature.

lib/presentation/providers/downloads_provider.dart

@@ -166,12 +166,9 @@ class DownloadsProvider with ChangeNotifier {
     notifyListeners();
   }
 
-  void _setError(String? error) {
-    _error = error;
-    notifyListeners();
-  }
-}? error) {
+  void _setError(String? error, [String? stackTrace]) {
     _error = error;
+    _stackTrace = stackTrace;
     notifyListeners();
   }
 }