fix(Core/Movement): creatures should not cast while moving (#9141)

- Closes #8843

src/server/game/Entities/Unit/Unit.cpp

@@ -3683,6 +3683,30 @@ int32 Unit::GetCurrentSpellCastTime(uint32 spell_id) const
     return 0;
 }
 
+bool Unit::IsMovementPreventedByCasting() const
+{
+    // can always move when not casting
+    if (!HasUnitState(UNIT_STATE_CASTING))
+    {
+        return false;
+    }
+
+    // channeled spells during channel stage (after the initial cast timer) allow movement with a specific spell attribute
+    if (Spell* spell = m_currentSpells[CURRENT_CHANNELED_SPELL])
+    {
+        if (spell->getState() != SPELL_STATE_FINISHED && spell->IsChannelActive())
+        {
+            if (spell->GetSpellInfo()->IsMoveAllowedChannel())
+            {
+                return false;
+            }
+        }
+    }
+
+    // prohibit movement for all other spell casts
+    return true;
+}
+
 bool Unit::CanMoveDuringChannel() const
 {
     if (Spell* spell = m_currentSpells[CURRENT_CHANNELED_SPELL])

src/server/game/Entities/Unit/Unit.h

@@ -2145,6 +2145,8 @@ public:
     [[nodiscard]] Spell* FindCurrentSpellBySpellId(uint32 spell_id) const;
     [[nodiscard]] int32 GetCurrentSpellCastTime(uint32 spell_id) const;
 
+    virtual bool IsMovementPreventedByCasting() const;
+
     ObjectGuid m_SummonSlot[MAX_SUMMON_SLOT];
     ObjectGuid m_ObjectSlot[MAX_GAMEOBJECT_SLOT];