chore: import upstream snapshot with attribution

dotnet/samples/Demos/VectorStoreRAG/UniqueKeyGenerator.cs

@@ -0,0 +1,18 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+namespace VectorStoreRAG;
+
+/// <summary>
+/// Class for generating unique keys via a provided function.
+/// </summary>
+/// <typeparam name="TKey">The type of key to generate.</typeparam>
+/// <param name="generator">The function to generate the key with.</param>
+internal sealed class UniqueKeyGenerator<TKey>(Func<TKey> generator)
+    where TKey : notnull
+{
+    /// <summary>
+    /// Generate a unique key.
+    /// </summary>
+    /// <returns>The unique key that was generated.</returns>
+    public TKey GenerateKey() => generator();
+}