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/Gumps/Guilds/New Guild System/BaseGuildGump.cs

@@ -7,12 +7,12 @@ namespace Server.Guilds
 {
     public abstract class BaseGuildGump : Gump
     {
+        public override bool Singleton => true;
+
         public BaseGuildGump(PlayerMobile pm, Guild g, int x = 10, int y = 10) : base(x, y)
         {
             guild = g;
             player = pm;
-
-            pm.CloseGump<BaseGuildGump>();
         }
 
         protected Guild guild { get; }