Fix ElasticWrapPanel not skipping hidden children when IsFillHorizontal and ItemWidth are set (#896)

* Initial plan

* Fix ElasticWrapPanel to skip invisible children in MeasureOverride and ArrangeOverride

Co-authored-by: rabbitism <14807942+rabbitism@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: rabbitism <14807942+rabbitism@users.noreply.github.com>

src/Ursa/Controls/Panels/ElasticWrapPanel.cs

@@ -117,6 +117,7 @@ public class ElasticWrapPanel : WrapPanel
 
         foreach (var child in children)
         {
+            if (!child.IsVisible) continue;
             UVSize sz;
             if (GetIsFixToRB(child))
             {
@@ -258,6 +259,7 @@ public class ElasticWrapPanel : WrapPanel
         var children = Children;
         foreach (var child in children)
         {
+            if (!child.IsVisible) continue;
             UVSize sz;
             if (GetIsFixToRB(child))
             {

tests/HeadlessTest.Ursa/Controls/ElasticWrapPanelTests/Tests.cs

@@ -216,4 +216,66 @@ public class Tests
         window.UpdateLayout();
         Assert.Equal(4, panel2.LineCount); // 1 item per line, 4 items total = 4 lines
     }
+
+    [AvaloniaFact]
+    public void HiddenItem_IsSkipped_WithItemWidth()
+    {
+        var window = new Window();
+        var panel = new ElasticWrapPanel
+        {
+            Width = 400,
+            Height = 400,
+            Orientation = Orientation.Horizontal,
+            ItemWidth = 100,
+            IsFillHorizontal = true,
+        };
+
+        // Add 4 items: item[1] is hidden
+        for (int i = 0; i < 4; i++)
+        {
+            var rect = new Rectangle
+            {
+                Width = 100,
+                Height = 100,
+                IsVisible = i != 1,
+            };
+            panel.Children.Add(rect);
+        }
+
+        window.Content = panel;
+        window.Show();
+
+        // 3 visible items of width 100 fit on one line in a 400-wide panel
+        Assert.Equal(1, panel.LineCount);
+    }
+
+    [AvaloniaFact]
+    public void HiddenItem_IsSkipped_WithoutItemWidth()
+    {
+        var window = new Window();
+        var panel = new ElasticWrapPanel
+        {
+            Width = 400,
+            Height = 400,
+            Orientation = Orientation.Horizontal,
+        };
+
+        // Add 4 items: item[1] is hidden
+        for (int i = 0; i < 4; i++)
+        {
+            var rect = new Rectangle
+            {
+                Width = 100,
+                Height = 100,
+                IsVisible = i != 1,
+            };
+            panel.Children.Add(rect);
+        }
+
+        window.Content = panel;
+        window.Show();
+
+        // 3 visible items of width 100 fit on one line in a 400-wide panel
+        Assert.Equal(1, panel.LineCount);
+    }
 }