feat: implement verificationcodeitem and corresponding delete operation.

demo/Ursa.Demo/ViewModels/VerificationCodeDemoViewModel.cs

@@ -1,8 +1,26 @@
-using CommunityToolkit.Mvvm.ComponentModel;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using System.Windows.Input;
+using Avalonia.Collections;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Ursa.Controls;
 
 namespace Ursa.Demo.ViewModels;
 
 public class VerificationCodeDemoViewModel: ObservableObject
 {
-    
+    public ICommand CompleteCommand { get; set; }
+
+    public VerificationCodeDemoViewModel()
+    {
+        CompleteCommand = new AsyncRelayCommand<IList<string>>(OnComplete);
+    }
+
+    private async Task OnComplete(IList<string>? obj)
+    {
+        if (obj is null) return;
+        var code = string.Join("", obj);
+        await MessageBox.ShowOverlayAsync(code);
+    }
 }