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/Spells/Ninjitsu/AnimalForm.cs

@@ -143,7 +143,6 @@ public class AnimalForm : NinjaSpell
                 var lastAnimalForm = GetLastAnimalForm(Caster);
                 if (Caster is PlayerMobile && lastAnimalForm == -1 && !_wasMoving && !CasterIsMoving())
                 {
-                    Caster.CloseGump<AnimalFormGump>();
                     Caster.SendGump(new AnimalFormGump(Caster, Entries, this));
                 }
                 else if (Morph(Caster, lastAnimalForm) == MorphResult.Fail)
@@ -361,6 +360,8 @@ public class AnimalForm : NinjaSpell
         private readonly AnimalForm _spell;
         private readonly AnimalFormEntry[] _entries;
 
+        public override bool Singleton => true;
+
         public AnimalFormGump(Mobile caster, AnimalFormEntry[] entries, AnimalForm spell) : base(50, 50)
         {
             _caster = caster;