Implement BenchmarkService with generateReport and pollUpdates methods

This commit introduces the `BenchmarkService` class, which encapsulates API calls related to benchmarking operations. The class includes two methods:

1. `generateReport`: Takes a `ReportRequestBody` object as input and performs a POST request to the `/reports` URL, serializing the object to JSON format.
2. `pollUpdates`: Accepts a UNIX UTC timestamp as an argument and performs a GET request to the `/updates?last_update_time=<timestamp>` URL.

Both methods use the `RestApiUtility` for making HTTP requests and are designed to work with different base URLs, controlled by the `ApiType` enum.

frontend/lib/services/benchmark_service.dart

@@ -0,0 +1,35 @@
+import 'dart:async';
+import 'package:auto_gpt_flutter_client/models/benchmark_service/report_request_body.dart';
+import 'package:auto_gpt_flutter_client/utils/rest_api_utility.dart';
+import 'package:auto_gpt_flutter_client/models/benchmark_service/api_type.dart';
+
+class BenchmarkService {
+  final RestApiUtility api;
+
+  BenchmarkService(this.api);
+
+  /// Generates a report using POST REST API at the /reports URL.
+  ///
+  /// [reportRequestBody] is a Map representing the request body for generating a report.
+  Future<Map<String, dynamic>> generateReport(
+      ReportRequestBody reportRequestBody) async {
+    try {
+      return await api.post('reports', reportRequestBody.toJson(),
+          apiType: ApiType.benchmark);
+    } catch (e) {
+      throw Exception('Failed to generate report: $e');
+    }
+  }
+
+  /// Polls for updates using the GET REST API at the /updates?last_update_time=TIMESTAMP URL.
+  ///
+  /// [lastUpdateTime] is the UNIX UTC timestamp for last update time.
+  Future<Map<String, dynamic>> pollUpdates(int lastUpdateTime) async {
+    try {
+      return await api.get('updates?last_update_time=$lastUpdateTime',
+          apiType: ApiType.benchmark);
+    } catch (e) {
+      throw Exception('Failed to poll updates: $e');
+    }
+  }
+}