feat: add inital in memory dispatcher

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

src/request.tests/_fixtures/ExplicitGenericStreamHandler.cs

@@ -0,0 +1,12 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+namespace Geekeey.Request.Tests;
+
+public class ExplicitGenericStreamHandler<T> : IStreamRequestHandler<ExplicitGenericStreamRequest, string>
+{
+	async IAsyncEnumerable<string> IStreamRequestHandler<ExplicitGenericStreamRequest, string>.HandleAsync(ExplicitGenericStreamRequest request, [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken ct)
+	{
+		yield return $"{request.Value}-ExplicitHandled";
+	}
+}