Seal/abstract/virtual everything (#6739)

Content.Shared/Item/ItemSystem.cs

@@ -7,7 +7,7 @@ using Robust.Shared.Localization;
 
 namespace Content.Shared.Item
 {
-    public class ItemSystem : EntitySystem
+    public sealed class ItemSystem : EntitySystem
     {
         public override void Initialize()
         {

Content.Shared/Item/PickupAttemptEvent.cs

@@ -5,7 +5,7 @@ namespace Content.Shared.Item
     /// <summary>
     /// Raised on a *mob* when it tries to pickup something
     /// </summary>
-    public class PickupAttemptEvent : CancellableEntityEventArgs
+    public sealed class PickupAttemptEvent : CancellableEntityEventArgs
     {
         public PickupAttemptEvent(EntityUid uid)
         {

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;