refactor(chess): 重构象棋程序基础结构,使用Nullable重构核心代码

- 更新了多个文件的代码结构和类型定义，提高了代码的健壮性和可维护性
- 优化了事件处理、棋子管理和移动逻辑，为后续功能扩展打下坚实基础
- 修复了一些潜在的空指针异常问题，提高了程序的稳定性
- 修复部分bug

Scripts/Lib/gdws.cs

@@ -2,16 +2,16 @@ using Godot;
 using Godot.Collections;
 
 public partial class EventDrivenWebSocket : WebSocketPeer {
-    public delegate void WebSocketEventHandler(string eventName, params object[] args);
+    public delegate void WebSocketEventHandler(string eventName, params object[]? args);
     public delegate void WSBinMsgEventHandler(byte[] args);
     public delegate void WSMsgEventHandler(string args);
 
-    public event WebSocketEventHandler OnOpen;
-    public event WSBinMsgEventHandler OnMessage;
-    public event WSMsgEventHandler OnText;
-    public event WSBinMsgEventHandler OnBinary;
-    public event WebSocketEventHandler OnClose;
-    public event WebSocketEventHandler OnError;
+    public event WebSocketEventHandler? OnOpen;
+    public event WSBinMsgEventHandler? OnMessage;
+    public event WSMsgEventHandler? OnText;
+    public event WSBinMsgEventHandler? OnBinary;
+    public event WebSocketEventHandler? OnClose;
+    public event WebSocketEventHandler? OnError;
 
     private bool isConnected = false;
     private bool isCloseEventFired = false;
@@ -32,7 +32,7 @@ public partial class EventDrivenWebSocket : WebSocketPeer {
     }
 
     public void ConnectToUrlEx(string url, double delayTime = 3,
-        TlsOptions tlsClientOptions = null) {
+        TlsOptions? tlsClientOptions = null) {
         if (connectingTime >= 0) {
             return;
         }