Seal/abstract/virtual everything (#6739)

Content.Shared/Damage/Systems/DamageableSystem.cs

@@ -10,7 +10,7 @@ using Robust.Shared.Prototypes;
 
 namespace Content.Shared.Damage
 {
-    public class DamageableSystem : EntitySystem
+    public sealed class DamageableSystem : EntitySystem
     {
         [Dependency] private readonly IPrototypeManager _prototypeManager = default!;
 
@@ -220,7 +220,7 @@ namespace Content.Shared.Damage
     ///
     ///     For example, armor.
     /// </summary>
-    public class DamageModifyEvent : EntityEventArgs, IInventoryRelayEvent
+    public sealed class DamageModifyEvent : EntityEventArgs, IInventoryRelayEvent
     {
         // Whenever locational damage is a thing, this should just check only that bit of armour.
         public SlotFlags TargetSlots { get; } = ~SlotFlags.POCKET;
@@ -233,7 +233,7 @@ namespace Content.Shared.Damage
         }
     }
 
-    public class DamageChangedEvent : EntityEventArgs
+    public sealed class DamageChangedEvent : EntityEventArgs
     {
         /// <summary>
         ///     This is the component whose damage was changed.