feat: add auto tick sample.

demo/Ursa.Demo/Pages/ClockDemo.axaml

@@ -5,10 +5,14 @@
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
     xmlns:u="https://irihi.tech/ursa"
+    xmlns:vm="clr-namespace:Ursa.Demo.ViewModels"
+    x:DataType="vm:ClockDemoViewModel"
+    x:CompileBindings="True"
     d:DesignHeight="450"
     d:DesignWidth="800"
+    
     mc:Ignorable="d">
     <Grid>
-        <u:Clock HorizontalAlignment="Left"></u:Clock>
+        <u:Clock HorizontalAlignment="Left" Time="{Binding Time}"></u:Clock>
     </Grid>
 </UserControl>

demo/Ursa.Demo/ViewModels/ClockDemoViewModel.cs

@@ -1,6 +1,31 @@
-namespace Ursa.Demo.ViewModels;
+using System;
+using System.Timers;
+using CommunityToolkit.Mvvm.ComponentModel;
 
-public class ClockDemoViewModel
+namespace Ursa.Demo.ViewModels;
+
+public partial class ClockDemoViewModel: ObservableObject, IDisposable
 {
+    private Timer _timer;
     
+    [ObservableProperty] private DateTime _time;
+    public ClockDemoViewModel()
+    {
+        Time = DateTime.Now;
+        _timer = new Timer(1000);
+        _timer.Elapsed += TimerOnElapsed;
+        _timer.Start();
+    }
+
+    private void TimerOnElapsed(object? sender, ElapsedEventArgs e)
+    {
+        Time = DateTime.Now;
+    }
+
+    public void Dispose()
+    {
+        _timer.Stop();
+        _timer.Elapsed -= TimerOnElapsed;
+        _timer.Dispose();
+    }
 }