feat: add inital in memory dispatcher

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

src/request.tests/_fixtures/BaseScalarHandler.cs

@@ -0,0 +1,10 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+namespace Geekeey.Request.Tests;
+
+public abstract class BaseScalarHandler<TRequest> : IScalarRequestHandler<TRequest, string>
+	where TRequest : IScalarRequest<string>
+{
+	public abstract Task<string> HandleAsync(TRequest request, CancellationToken cancellationToken);
+}