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/AddonGenerator.cs

@@ -307,9 +307,10 @@ public class AddonGenerator
         private const int GreenHue = 0x40;
         private readonly PickerState _state;
 
+        public override bool Singleton => true;
+
         public InternalGump(Mobile m, PickerState state) : base(100, 50)
         {
-            m.CloseGump<InternalGump>();
             _state = state;
             MakeGump();
         }