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/get_editor_interface.gd

@@ -0,0 +1,6 @@
+# This file is here so we can load it only when we are in the editor so that
+# other places do not have to have "EditorInterface" in them, which causes a
+# parser error when loaded outside of the editor.  The things we have to do in
+# order to test things is annoying.
+func get_it():
+	return EditorInterface