优化更新代码，添加界面功能并整合

WPFluent/Controls/PendingBox/IPendingHandler.cs

@@ -0,0 +1,24 @@
+using System;
+
+namespace WPFluent.Controls;
+
+public interface IPendingHandler : IDisposable
+{
+    public event EventHandler? Closed;
+
+    public event EventHandler? Cancel;
+
+    public DateTime StartTime { get; set; }
+
+    public string? Message { get; set; }
+
+    public bool IsShowCancel { get; set; }
+
+    public bool Canceled { get; }
+
+    public void Show();
+
+    public bool? ShowDialog();
+
+    public void Close();
+}