feat(network): 默认心跳处理器设置 30 秒间隔

为 DefaultPacketHeartBeatHandler 覆盖 HeartBeatInterval 属性，将默认心跳间隔设置为 30 秒。

Author: AlianBlank

Assets/Hotfix/Network/DefaultPacketHeartBeatHandler.cs

@@ -6,6 +6,8 @@ namespace Hotfix.Network
 {
     public sealed class DefaultPacketHeartBeatHandler : BasePacketHeartBeatHandler
     {
+        public override float HeartBeatInterval { get; } = 30;
+
         public override MessageObject Handler()
         {
             var reqHeartBeat = new ReqHeartBeat