feat: add demo, fix clear button of TimeRangePicker.

demo/Ursa.Demo/ViewModels/TimeRangePickerDemoViewModel.cs

@@ -0,0 +1,16 @@
+using System;
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace Ursa.Demo.ViewModels;
+
+public partial class TimeRangePickerDemoViewModel: ObservableObject
+{
+    [ObservableProperty] private TimeSpan? _startTime;
+    [ObservableProperty] private TimeSpan? _endTime;
+
+    public TimeRangePickerDemoViewModel()
+    {
+        StartTime = new TimeSpan(8, 21, 0);
+        EndTime = new TimeSpan(18, 22, 0);
+    }
+}