chore(wip): upgrade dependencies, begin refactor

frontend/lib/core/dio_client.dart

@@ -0,0 +1,16 @@
+import 'package:dio/dio.dart';
+
+class DioClient {
+  final Dio dio;
+
+  DioClient({required String baseUrl}): dio = Dio(BaseOptions(
+    baseUrl: baseUrl,
+    connectTimeout: const Duration(seconds: 5),
+    receiveTimeout: const Duration(seconds: 120),
+    // also accept 500 errors, since we cannot rule out that the server is at fault. We still want to gracefully handle these errors
+    validateStatus: (status) => status! <= 500,
+    receiveDataWhenStatusError: true,
+    contentType: Headers.jsonContentType,
+    responseType: ResponseType.json,
+  ));
+}