feat: add pub/sub support to dispatcher

Notifications are broadcast to zero or more handlers with configurable
publishing strategies (sequential or parallel) and pipeline behavior
support.

src/request.dispatcher/INotificationPublisher.cs

@@ -0,0 +1,20 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+namespace Geekeey.Request.Dispatcher;
+
+/// <summary>
+/// Defines a strategy for publishing notifications to registered handlers.
+/// </summary>
+public interface INotificationPublisher
+{
+	/// <summary>
+	/// Publishes the specified notification to the given collection of handlers.
+	/// </summary>
+	/// <typeparam name="TNotification">The type of notification being published. Must implement <see cref="INotification"/>.</typeparam>
+	/// <param name="handlers">The list of handlers to invoke.</param>
+	/// <param name="notification">The notification instance to publish.</param>
+	/// <param name="cancellationToken">A token to monitor for cancellation requests.</param>
+	/// <returns>A task representing the asynchronous publish operation.</returns>
+	Task PublishAsync<TNotification>(IEnumerable<INotificationHandler<TNotification>> handlers, TNotification notification, CancellationToken cancellationToken) where TNotification : INotification;
+}