feat: 重构棋盘逻辑和游戏流程,将引擎版本提升至4.3

- 重构了 VirtualBoard 类，优化了棋盘操作和事件处理
- 重写了 ChessPiece 类，增加了事件处理和虚拟棋子逻辑
- 更新了 ChessGame 控制器，增加了结束回合功能和对话框
- 调整了场景布局和资源引用
- 清理了冗余代码和注释

Scripts/Utilities/VirtualPiece.cs

@@ -0,0 +1,40 @@
+// using System.Numerics;
+using Godot;
+
+using System;
+
+public class VirtualPiece  {
+    private Vector2 pos; // 注意这个坐标的非像素坐标而是棋盘坐标
+    
+    private string name;
+    private bool isSelected;
+    public object data;
+
+    public event Action<Vector2> OnMove;
+    public event Action<bool> OnSelected;
+
+    public void Move(Vector2 pos) {
+        this.pos = pos;
+        OnMove?.Invoke(pos);
+    }
+
+    public Vector2 Pos() {
+        return pos;
+    }
+
+    public void Selected(bool isSelected) {
+        if (this.isSelected != isSelected) {
+            OnSelected?.Invoke(isSelected);
+            this.isSelected = isSelected;
+        }
+    }
+
+    public bool IsSelected() {
+        return isSelected;
+    }
+
+    public VirtualPiece(string name = "", Vector2 pos = new Vector2()) {
+        this.name = name;
+        this.pos = pos;
+    }
+}