feat: add inital in memory dispatcher

Add a simple in memory dispatcher for scalar requests and stream request.

src/request.tests/_fixtures/DerivedStreamHandler.cs

@@ -0,0 +1,13 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+namespace Geekeey.Request.Tests;
+
+public class DerivedStreamHandler : BaseStreamHandler<DerivedStreamRequest>
+{
+	public override async IAsyncEnumerable<string> HandleAsync(DerivedStreamRequest request, [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken)
+	{
+		yield return $"Derived: {request.Value}-0";
+		yield return $"Derived: {request.Value}-1";
+	}
+}