Seal/abstract/virtual everything (#6739)

Content.Client/Module/ClientModuleManager.cs

@@ -7,7 +7,7 @@ namespace Content.Client.Module
     /// Provides simple way for shared code to check if it's being run by
     /// the client of the server.
     /// </summary>
-    public class ClientModuleManager : IModuleManager
+    public sealed class ClientModuleManager : IModuleManager
     {
         bool IModuleManager.IsClientModule => true;
         bool IModuleManager.IsServerModule => false;