feat(Core/Spells): Implement OnSpellCastFinished hook (#22941)

Co-authored-by: Ovahlord <dreadkiller@gmx.de>

src/server/game/Spells/Spell.h

@@ -92,6 +92,13 @@ enum SpellRangeFlag
     SPELL_RANGE_RANGED              = 2,     //hunter range and ranged weapon
 };
 
+enum SpellFinishReason : uint8
+{
+    SPELL_FINISHED_SUCCESSFUL_CAST     = 0, // spell has sucessfully launched
+    SPELL_FINISHED_CANCELED            = 1, // spell has been canceled (interrupts)
+    SPELL_FINISHED_CHANNELING_COMPLETE = 2  // spell channeling has been finished
+};
+
 struct SpellDestination
 {
     SpellDestination();