Seal/abstract/virtual everything (#6739)

Content.Server/PneumaticCannon/PneumaticCannonComponent.cs

@@ -14,7 +14,7 @@ namespace Content.Server.PneumaticCannon
     // TODO: ideally, this and most of the actual firing code doesn't need to exist, and guns can be flexible enough
     // to handle shooting things that aren't ammo (just firing any entity)
     [RegisterComponent, Friend(typeof(PneumaticCannonSystem))]
-    public class PneumaticCannonComponent : Component
+    public sealed class PneumaticCannonComponent : Component
     {
         [ViewVariables]
         public ContainerSlot GasTankSlot = default!;

Content.Server/PneumaticCannon/PneumaticCannonSystem.cs

@@ -29,7 +29,7 @@ using Robust.Shared.Random;
 
 namespace Content.Server.PneumaticCannon
 {
-    public class PneumaticCannonSystem : EntitySystem
+    public sealed class PneumaticCannonSystem : EntitySystem
     {
         [Dependency] private readonly IRobustRandom _random = default!;
         [Dependency] private readonly StunSystem _stun = default!;