fix: 修复聊天系统编译错误

- 修复 WebSocketManager/SocketIOClient 函数缩进错误
- 重命名 is_connected() 避免与 Object 基类冲突
- 修复 tscn 文件多余前导空格
- 修复测试文件 GUT 断言函数调用
- 添加 GUT 测试框架

addons/gut/images/HSplitContainer.svg

@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   width="16"
+   height="16"
+   version="1.1"
+   id="svg4434"
+   sodipodi:docname="HSplitContainer.svg"
+   inkscape:version="1.2.2 (b0a84865, 2022-12-01)"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:svg="http://www.w3.org/2000/svg">
+  <defs
+     id="defs4438" />
+  <sodipodi:namedview
+     id="namedview4436"
+     pagecolor="#505050"
+     bordercolor="#eeeeee"
+     borderopacity="1"
+     inkscape:showpageshadow="0"
+     inkscape:pageopacity="0"
+     inkscape:pagecheckerboard="0"
+     inkscape:deskcolor="#505050"
+     showgrid="false"
+     inkscape:zoom="14.75"
+     inkscape:cx="8"
+     inkscape:cy="8"
+     inkscape:window-width="1309"
+     inkscape:window-height="456"
+     inkscape:window-x="271"
+     inkscape:window-y="1388"
+     inkscape:window-maximized="0"
+     inkscape:current-layer="svg4434" />
+  <path
+     fill="#8eef97"
+     d="M3 1a2 2 0 0 0-2 2v10a2 2 0 0 0 2 2h10a2 2 0 0 0 2-2V3a2 2 0 0 0-2-2zm0 2h4v3L5 8l2 2v3H3zm6 0h4v10H9v-3l2-2-2-2z"
+     id="path4432"
+     style="fill-opacity:1.0;fill:#ffffff" />
+</svg>