Match buff-based immunity via C_UnitAuras.GetAuraDataBySpellName

Replaces the 32-slot UnitBuff + C_Spell.GetSpellName name-compare loop with a
single ClassicAPI.GetAuraDataBySpellName(unit, name, "HELPFUL") lookup.
Locale-identical to the old compare (both use the localized Spell.dbc name).
Wrapper added next to GetUnitAuraBySpellID.

ClassicAPI.lua

@@ -95,6 +95,19 @@ function API.GetUnitAuraBySpellID(unit, spellID, filter)
     return C_UnitAuras.GetUnitAuraBySpellID(unit, spellID, filter)
 end
 
+-- First matching aura on `unit` by spell NAME, or nil. Same whole-array search as
+-- GetUnitAuraBySpellID; the name is case-sensitive and locale-resolved, so pass it
+-- in the client's locale (what C_Spell.GetSpellName returns). filter
+-- ("HELPFUL"/"HARMFUL") restricts the search. Prefer the by-ID variant for
+-- portability where a spellID is known.
+function API.GetAuraDataBySpellName(unit, spellName, filter)
+    if not unit or not spellName or spellName == "" then return nil end
+    if type(C_UnitAuras) ~= "table" or type(C_UnitAuras.GetAuraDataBySpellName) ~= "function" then
+        return nil
+    end
+    return C_UnitAuras.GetAuraDataBySpellName(unit, spellName, filter)
+end
+
 --------------------------------------------------------------------------------
 -- GetUnitSpeed
 --------------------------------------------------------------------------------

Utility.lua

@@ -8800,23 +8800,12 @@ function CleveRoids.CheckImmunity(unitId, spellOrSchool)
             end
         end
 
-        -- Check buff-based immunity (if NPC has the required buff)
+        -- Check buff-based immunity (if NPC has the required buff). One by-name
+        -- lookup across the unit's buffs via C_UnitAuras -- no 32-slot scan.
         if immunityData.buff then
-            local requiredBuff = immunityData.buff
-
-            -- Check target's buffs
-            for i = 1, 32 do
-                local texture, stacks, spellID = UnitBuff(unitId, i)
-                if not texture then break end
-
-                if spellID then
-                    local buffName = C_Spell.GetSpellName(spellID)
-                    if buffName and buffName == requiredBuff then
-                        return true
-                    end
-                end
+            if CleveRoids.ClassicAPI.GetAuraDataBySpellName(unitId, immunityData.buff, "HELPFUL") then
+                return true
             end
-
             -- Buff not found, not currently immune
             return false
         end