refactor(state): 修改状态机接口返回类型支持链式调用

- 将Register方法返回类型从void改为IStateMachine
- 将Unregister方法返回类型从void改为IStateMachine
- 在实现类中添加return this语句
- 更新接口定义以匹配新的返回类型
- 实现链式调用功能提升API易用性

GFramework.Core.Abstractions/state/IStateMachine.cs

@@ -17,13 +17,13 @@ public interface IStateMachine
     /// 注册一个状态到状态机中
     /// </summary>
     /// <param name="state">要注册的状态实例</param>
-    void Register(IState state);
+    IStateMachine Register(IState state);
 
     /// <summary>
     /// 从状态机中注销指定类型的状态
     /// </summary>
     /// <typeparam name="T">要注销的状态类型，必须实现IState接口</typeparam>
-    void Unregister<T>() where T : IState;
+    IStateMachine Unregister<T>() where T : IState;
 
     /// <summary>
     /// 检查是否可以切换到指定类型的状态

GFramework.Core/state/StateMachine.cs

@@ -24,24 +24,26 @@ public class StateMachine(int maxHistorySize = 10) : IStateMachine
     /// 注册一个状态到状态机中
     /// </summary>
     /// <param name="state">要注册的状态实例</param>
-    public void Register(IState state)
+    public IStateMachine Register(IState state)
     {
         lock (_lock)
         {
             States[state.GetType()] = state;
         }
+
+        return this;
     }
 
     /// <summary>
     /// 从状态机中注销指定类型的状态
     /// </summary>
     /// <typeparam name="T">要注销的状态类型</typeparam>
-    public void Unregister<T>() where T : IState
+    public IStateMachine Unregister<T>() where T : IState
     {
         lock (_lock)
         {
             var type = typeof(T);
-            if (!States.TryGetValue(type, out var state)) return;
+            if (!States.TryGetValue(type, out var state)) return this;
 
             // 如果当前状态是要注销的状态，则先执行退出逻辑
             if (Current == state)
@@ -60,6 +62,8 @@ public class StateMachine(int maxHistorySize = 10) : IStateMachine
 
             States.Remove(type);
         }
+
+        return this;
     }
 
     /// <summary>