Seal/abstract/virtual everything (#6739)

Content.Shared/Item/SharedItemComponent.cs

@@ -20,7 +20,7 @@ namespace Content.Shared.Item
     ///    Players can pick up, drop, and put items in bags, and they can be seen in player's hands.
     /// </summary>
     [NetworkedComponent()]
-    public class SharedItemComponent : Component, IInteractHand
+    public abstract class SharedItemComponent : Component, IInteractHand
     {
         [Dependency] private readonly IEntityManager _entMan = default!;
 
@@ -136,7 +136,7 @@ namespace Content.Shared.Item
     }
 
     [Serializable, NetSerializable]
-    public class ItemComponentState : ComponentState
+    public sealed class ItemComponentState : ComponentState
     {
         public int Size { get; }
         public string? EquippedPrefix { get; }
@@ -157,7 +157,7 @@ namespace Content.Shared.Item
     ///     that it can properly update its sprite/GUI.
     /// </summary>
     [Serializable, NetSerializable]
-    public class ItemPrefixChangeEvent : EntityEventArgs
+    public sealed class ItemPrefixChangeEvent : EntityEventArgs
     {
         public readonly EntityUid Item;
         public readonly string ContainerId;