feat: add inital in memory dispatcher

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

src/request.tests/_fixtures/ConstrainedStreamHandler.cs

@@ -0,0 +1,14 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+namespace Geekeey.Request.Tests;
+
+public class ConstrainedStreamHandler<TRequest> : IStreamRequestHandler<TRequest, string>
+	where TRequest : ConstrainedStreamRequest
+{
+	public async IAsyncEnumerable<string> HandleAsync(TRequest request, [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken)
+	{
+		yield return $"{request.Value}-Constrained-0";
+		yield return $"{request.Value}-Constrained-1";
+	}
+}