Introduce ChatService Class for Chat Operations

This commit adds a new ChatService class to handle all chat-related operations, including steps and artifacts.

- Implemented methods for executing a step within a task (executeStep).
- Added functionality to retrieve details for a specific step (getStepDetails).
- Enabled listing all steps for a specific task with optional pagination (listTaskSteps).
- Laid groundwork for artifact uploading (uploadArtifact) and downloading (downloadArtifact), though these are not implemented yet.

By encapsulating these operations within the ChatService class, this commit provides a clean and centralized way to interact with the backend for chat functionalities, making the application more maintainable and easier to extend.

lib/services/chat_service.dart

@@ -0,0 +1,70 @@
+import 'dart:io';
+import 'package:auto_gpt_flutter_client/models/step_request_body.dart';
+import 'package:auto_gpt_flutter_client/utils/rest_api_utility.dart';
+
+/// Service class for performing chat-related operations.
+class ChatService {
+  final RestApiUtility api;
+
+  ChatService(this.api);
+
+  /// Executes a step in a specific task.
+  ///
+  /// [taskId] is the ID of the task.
+  /// [stepRequestBody] is a Map representing the request body for executing a step.
+  Future<Map<String, dynamic>> executeStep(
+      String taskId, StepRequestBody stepRequestBody) async {
+    try {
+      return await api.post(
+          'agent/tasks/$taskId/steps', stepRequestBody.toJson());
+    } catch (e) {
+      throw Exception('Failed to execute step: $e');
+    }
+  }
+
+  /// Gets details about a specific task step.
+  ///
+  /// [taskId] is the ID of the task.
+  /// [stepId] is the ID of the step.
+  Future<Map<String, dynamic>> getStepDetails(
+      String taskId, String stepId) async {
+    try {
+      return await api.get('agent/tasks/$taskId/steps/$stepId');
+    } catch (e) {
+      throw Exception('Failed to get step details: $e');
+    }
+  }
+
+  /// Lists all steps for a specific task.
+  ///
+  /// [taskId] is the ID of the task.
+  /// [currentPage] and [pageSize] are optional pagination parameters.
+  Future<List<dynamic>> listTaskSteps(String taskId,
+      {int currentPage = 1, int pageSize = 10}) async {
+    try {
+      return await api.getList(
+          'agent/tasks/$taskId/steps?current_page=$currentPage&page_size=$pageSize');
+    } catch (e) {
+      throw Exception('Failed to list task steps: $e');
+    }
+  }
+
+  /// Uploads an artifact for a specific task.
+  ///
+  /// [taskId] is the ID of the task.
+  /// [artifactFile] is the File to be uploaded.
+  /// [uri] is the URI of the artifact.
+  Future<Map<String, dynamic>> uploadArtifact(
+      String taskId, File artifactFile, String uri) async {
+    return Future.value({'status': 'Not implemented yet'});
+  }
+
+  /// Downloads a specific artifact.
+  ///
+  /// [taskId] is the ID of the task.
+  /// [artifactId] is the ID of the artifact.
+  Future<Map<String, dynamic>> downloadArtifact(
+      String taskId, String artifactId) async {
+    return Future.value({'status': 'Not implemented yet'});
+  }
+}