feat: add input mode, allow null ipaddress, refactor code for better readbility.

demo/Ursa.Demo/Pages/IPv4BoxDemo.axaml

@@ -17,19 +17,27 @@
             Name="format"
             Margin="0,0,0,50"
             Content="Show Leading Zeroes" />
-
+        <TextBlock Classes="" Text="Normal" />
         <u:IPv4Box
             Name="box"
             Width="200"
             ShowLeadingZero="{Binding #format.IsChecked}" />
+
         <TextBlock Text="IP: " />
         <TextBlock Text="{Binding #box.IPAddress}" />
+        <TextBlock Classes="" Text="Fast input" />
+        <u:IPv4Box
+            Width="200"
+            InputMode="Fast"
+            ShowLeadingZero="{Binding #format.IsChecked}" />
 
+        <TextBlock Classes="" Text="Binding From Source" />
         <RepeatButton Command="{Binding ChangeAddress}" Content="Random" />
         <u:IPv4Box
             Width="200"
             IPAddress="{Binding Address}"
             ShowLeadingZero="{Binding #format.IsChecked}" />
+        <TextBlock Classes="" Text="Disabled" />
         <u:IPv4Box Width="200" IsEnabled="False" />
     </StackPanel>
 </UserControl>