feat: finish int implementation.

src/Ursa/Controls/NumericUpDown/ValueChangedEventArgs.cs

@@ -0,0 +1,15 @@
+using Avalonia.Interactivity;
+
+namespace Ursa.Controls;
+
+public class ValueChangedEventArgs<T>: RoutedEventArgs where T: struct, IComparable<T>
+{
+    public ValueChangedEventArgs(RoutedEvent routedEvent, T? oldValue, T? newValue): base(routedEvent)
+    {
+        OldValue = oldValue;
+        NewValue = newValue;
+    }
+    public T? OldValue { get; }
+    public T? NewValue { get; }
+    
+}