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/Engines/ConPVP/Gumps/DuelContextGump.cs

@@ -5,14 +5,17 @@ namespace Server.Engines.ConPVP
 {
     public class DuelContextGump : Gump
     {
+        public override bool Singleton => true;
+
         public DuelContextGump(Mobile from, DuelContext context) : base(50, 50)
         {
             From = from;
             Context = context;
 
-            from.CloseGump<RulesetGump>();
-            from.CloseGump<DuelContextGump>();
-            from.CloseGump<ParticipantGump>();
+            var gumps = from.GetGumps();
+
+            gumps.Close<RulesetGump>();
+            gumps.Close<ParticipantGump>();
 
             var count = context.Participants.Count;