Core/Spells: Implement spell queue

Port From (https://github.com/TrinityCore/TrinityCore/commit/27019a62a4294f8dd48d975f85b1907c5adee0e3)

Source/Game/Entities/Player/Player.Fields.cs

@@ -110,6 +110,7 @@ namespace Game.Entities
         public Spell m_spellModTakingSpell;
         uint m_oldpetspell;
         Dictionary<uint, StoredAuraTeleportLocation> m_storedAuraTeleportLocations = new();
+        SpellCastRequest _pendingSpellCastRequest;
 
         //Mail
         List<Mail> m_mail = new();