feat: Moves gumps out of the core (#1916)

> [!Important]
> **Developer Note**
> This code change will **completely move gumps out of the core**


### Summary

- Adds `GetGumps()` convenience which exposes methods to Find/Close/Send multiple gumps. This helper is a performance improvement by eliminating the Dictionary<Player, List> lookup for gumps.

Projects/UOContent/Commands/Object Creation/CategorizedAddGump.cs

@@ -34,14 +34,14 @@ namespace Server.Gumps
         private readonly Mobile m_Owner;
         private int m_Page;
 
+        public override bool Singleton => true;
+
         public CategorizedAddGump(Mobile owner) : this(owner, CAGCategory.Root)
         {
         }
 
         public CategorizedAddGump(Mobile owner, CAGCategory category, int page = 0) : base(GumpOffsetX, GumpOffsetY)
         {
-            owner.CloseGump<WhoGump>();
-
             m_Owner = owner;
             m_Category = category;