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/Items/Misc/PlayerBulletinBoards.cs

@@ -290,10 +290,10 @@ public class PlayerBBGump : Gump
     private BaseHouse _house;
     private int _page;
 
+    public override bool Singleton => true;
+
     public PlayerBBGump(Mobile from, BaseHouse house, BasePlayerBB board, int page) : base(50, 10)
     {
-        from.CloseGump<PlayerBBGump>();
-
         _page = page;
         _from = from;
         _house = house;