feat(TreeView): 增加 OverscanCount 支持

Author: ArgoZhang

src/BootstrapBlazor/Components/TreeView/TreeView.razor

@@ -47,7 +47,7 @@ else
         @if (IsVirtualize)
         {
             <div class="tree-root scroll is-virtual" tabindex="0">
-                <Virtualize ItemSize="RowHeight" OverscanCount="10" Items="@Rows">
+                <Virtualize ItemSize="RowHeight" OverscanCount="OverscanCount" Items="@Rows">
                     @RenderRow(context)
                 </Virtualize>
             </div>

src/BootstrapBlazor/Components/TreeView/TreeView.razor.cs

@@ -224,6 +224,13 @@ public partial class TreeView<TItem> : IModelEqualityComparer<TItem>
     [Parameter]
     public float RowHeight { get; set; } = 38f;
 
+    /// <summary>
+    /// Gets or sets the overscan count for virtual scrolling. Default is 10.
+    /// </summary>
+    /// <remarks>Effective when <see cref="IsVirtualize"/> is set to true.</remarks>
+    [Parameter]
+    public int OverscanCount { get; set; } = 10;
+
     /// <summary>
     /// Gets or sets the toolbar content template. Default is null.
     /// </summary>