Added missing LazyFetchEventArgs container

Source/Collections/LazyFetchEventArgs.cs

@@ -0,0 +1,54 @@
+#region Apache License 2.0
+/*
+Nuclex Foundation libraries for .NET
+Copyright (C) 2002-2025 Markus Ewald / Nuclex Development Labs
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+#endregion // Apache License 2.0
+
+using System;
+
+namespace Nuclex.Avalonia.Collections {
+
+  /// <summary>
+  ///   Argument container to report when items have been fetch by a lazy-loading collection
+  /// </summary>
+  public class LazyFetchEventArgs {
+
+    /// <summary>Initializes a new lazy-fetched item argument container</summary>
+    /// <param name="startIndex">Index of the first item that has been fetched</param>
+    /// <param name="count">Number of items that have been fetched</param>
+    public LazyFetchEventArgs(int startIndex, int count) {
+      this.startIndex = startIndex;
+      this.count = count;
+    }
+
+    /// <summary>Index of the first item that has been fetched</summary>
+    public int StartIndex {
+      get { return this.startIndex; }
+    }
+
+    /// <summary>Number of items that have been fetched</summary>
+    public int Count {
+      get { return this.count; }
+    }
+
+    /// <summary>Index of the first item that has been fetched</summary>
+    private int startIndex;
+    /// <summary>Number of items that have been fetched</summary>
+    private int count;
+
+  }
+
+} // namespace Nuclex.Avalonia.Collections