feat:增加消息记录功能

lib/models/chat_message.dart

@@ -0,0 +1,26 @@
+import 'package:json_annotation/json_annotation.dart';
+
+part 'chat_message.g.dart';
+
+@JsonSerializable()
+class ChatMessage {
+  final int msgId;
+  final int senderId;
+  final String content;
+  /// 消息类型（1文本 2图片 3语音）
+  final int msgType;
+  final DateTime createTime;
+
+  ChatMessage({
+    required this.msgId,
+    required this.senderId,
+    required this.content,
+    required this.msgType,
+    required this.createTime,
+  });
+
+  factory ChatMessage.fromJson(Map<String, dynamic> json) =>
+      _$ChatMessageFromJson(json);
+
+  Map<String, dynamic> toJson() => _$ChatMessageToJson(this);
+}