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/CreateGuildGump.cs

@@ -6,9 +6,10 @@ namespace Server.Guilds
 {
     public class CreateGuildGump : Gump
     {
+        public override bool Singleton => true;
+
         public CreateGuildGump(PlayerMobile pm, string guildName = "Guild Name", string guildAbbrev = "") : base(10, 10)
         {
-            pm.CloseGump<CreateGuildGump>();
             pm.CloseGump<BaseGuildGump>();
 
             AddPage(0);