fix: Magic NPCs now use spell range (#1870)

### Summary
- Drastically streamlines the spell targeting by collapsing the target classes into a single `SpellTarget<T>` class.
- Moves TargetRange to the spell itself so it can be used by MageAI.
- Changes range check in MageAI to use TargetRange. This should fix target acquisition bugs

Projects/UOContent/Engines/Factions/Mobiles/Guards/GuardAI.cs

@@ -487,7 +487,7 @@ namespace Server.Factions
                     {
                         targ.Invoke(m_Guard, toHarm);
                     }
-                    else if ((targ as ISpellTarget)?.Spell is DispelSpell)
+                    else if ((targ as ISpellTarget<Mobile>)?.Spell is DispelSpell)
                     {
                         targ.Cancel(m_Guard, TargetCancelType.Canceled);
                     }