refactor(profile): update ProfileRepository to include Ref for improved state management and enhance error handling in tests

flutter/lib/core/api/api_client.dart

@@ -1,5 +1,6 @@
 import 'dart:convert';
 
+import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:http/http.dart' as http;
 
 import 'api_exception.dart';
@@ -128,4 +129,8 @@ class ApiClient {
     if (parsedBody is String && parsedBody.trim().isNotEmpty) return parsedBody;
     return null;
   }
-}
+}
+
+final apiClientProvider = Provider<ApiClient>((ref) {
+  return ApiClient();
+});