Add EverythingServer sample (#151)

samples/EverythingServer/SubscriptionMessageSender.cs

@@ -0,0 +1,23 @@
+using Microsoft.Extensions.Hosting;
+using ModelContextProtocol;
+using ModelContextProtocol.Server;
+
+internal class SubscriptionMessageSender(IMcpServer server, HashSet<string> subscriptions) : BackgroundService
+{
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            foreach (var uri in subscriptions)
+            {
+                await server.SendNotificationAsync("notifications/resource/updated",
+                    new
+                    {
+                        Uri = uri,
+                    }, cancellationToken: stoppingToken);
+            }
+
+            await Task.Delay(5000, stoppingToken);
+        }
+    }
+}