feat: fix memory leakage.

demo/Ursa.Demo/Pages/DialogDemo.axaml

@@ -17,6 +17,10 @@
                 <Run Text="Result: "></Run>
                 <Run Text="{Binding Result}"></Run>
             </TextBlock>
+            <TextBlock>
+                <Run Text="Date: "></Run>
+                <Run Text="{Binding DialogViewModel.Date}"></Run>
+            </TextBlock>
             <Button Command="{Binding ShowGlobalDialogCommand}">Show Dialog</Button>
             <Button Command="{Binding ShowLocalOverlayDialogCommand}">Show Local Overlay Dialog</Button>
             <Button Command="{Binding ShowGlobalOverlayDialogCommand}"> Show Global Overlay Dialog </Button>