Add sealed services

Also fix a missing IDisposable

Akari.Prototype.Server/Services/AuthLifetimeService.cs

@@ -8,7 +8,7 @@ using System.Threading.Tasks;
 
 namespace Akari.Prototype.Server.Services
 {
-    public class AuthLifetimeService : IHostedService
+    public sealed class AuthLifetimeService : IHostedService, IDisposable
     {
         public static TimeSpan CleanupInterval => TimeSpan.FromSeconds(5);
         public static TimeSpan AuthLifetime => TimeSpan.FromSeconds(30);