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/Preferences.cs

@@ -179,6 +179,8 @@ namespace Server.Engines.ConPVP
         private readonly PreferencesEntry m_Entry;
         private int m_ColumnX = 12;
 
+        public override bool Singleton => true;
+
         public PreferencesGump(Mobile from, Preferences prefs) : base(50, 50)
         {
             m_Entry = prefs.Find(from);