前端：

1、优化消息排序逻辑
2、新增加载历史消息
3、修复已知问题
后端：
1、优化消息排序逻辑
2、增加用户信息缓存机制
3、修改日期类型为DateTimeOffset改善时区信息丢失问题
3、修复了已知问题
数据库：
1、新增SequenceId字段用于消息排序
2、新增ClientMsgId字段用于客户端消息回执

backend/IM_API/Hubs/ChatHub.cs

@@ -5,6 +5,7 @@ using IM_API.Dtos;
 using IM_API.Interface.Services;
 using IM_API.Models;
 using IM_API.Tools;
+using IM_API.VOs.Message;
 using Microsoft.AspNetCore.SignalR;
 using System.Security.Claims;
 
@@ -40,16 +41,16 @@ namespace IM_API.Hubs
             }
             await base.OnConnectedAsync();
         }
-        public async Task<HubResponse<MessageBaseDto?>> SendMessage(MessageBaseDto dto)
+        public async Task<HubResponse<MessageBaseVo?>> SendMessage(MessageBaseDto dto)
         {
             if (!Context.User.Identity.IsAuthenticated)
             {
                 await Clients.Caller.SendAsync("ReceiveMessage", new BaseResponse<object?>(CodeDefine.AUTH_FAILED));
                 Context.Abort();
-                return new HubResponse<MessageBaseDto?>(CodeDefine.AUTH_FAILED, "SendMessage");
+                return new HubResponse<MessageBaseVo?>(CodeDefine.AUTH_FAILED, "SendMessage");
             }
             var userIdStr = Context.User.FindFirstValue(ClaimTypes.NameIdentifier);
-            MessageBaseDto msgInfo = null;
+            MessageBaseVo? msgInfo = null;
             if(dto.ChatType == ChatType.PRIVATE)
             {
                 msgInfo = await _messageService.SendPrivateMessageAsync(int.Parse(userIdStr), dto.ReceiverId, dto);
@@ -58,7 +59,7 @@ namespace IM_API.Hubs
             {
                 msgInfo = await _messageService.SendGroupMessageAsync(int.Parse(userIdStr), dto.ReceiverId, dto);
             }
-            return new HubResponse<MessageBaseDto?>("SendMessage", msgInfo);
+            return new HubResponse<MessageBaseVo?>("SendMessage", msgInfo);
         }
         public async Task<HubResponse<object?>> ClearUnreadCount(int conversationId)
         {