refactor(core-tests): 简化状态机异步断言包装

- 简化 StateMachineSystemTests 中的 Task 异常断言包装

- 简化 StateMachineTests 中的异步异常断言包装并保持测试语义不变

GFramework.Core.Tests/State/StateMachineSystemTests.cs

@@ -138,7 +138,7 @@ public class StateMachineSystemTests
     [Test]
     public async Task DestroyAsync_Should_Not_Throw_Exception()
     {
-        Assert.That(async () => await _stateMachine!.DestroyAsync(), Throws.Nothing);
+        Assert.That(() => _stateMachine!.DestroyAsync(), Throws.Nothing);
     }
 
     /// <summary>

GFramework.Core.Tests/State/StateMachineTests.cs

@@ -216,7 +216,7 @@ public class StateMachineTests
     [Test]
     public void ChangeToAsync_ToUnregisteredState_Should_ThrowInvalidOperationException()
     {
-        Assert.ThrowsAsync<InvalidOperationException>(async () => await _stateMachine.ChangeToAsync<TestStateV2>());
+        Assert.ThrowsAsync<InvalidOperationException>(() => _stateMachine.ChangeToAsync<TestStateV2>());
     }
 
     /// <summary>
@@ -601,4 +601,4 @@ public static class StateMachineExtensions
                    .GetValue(stateMachine) is Dictionary<Type, IState> states &&
                states.ContainsKey(typeof(T));
     }
-}
+}