Finish the C_UnitAuras swap in CheckImmunity

CheckImmunity asks "is this NPC immune to that school, and if the entry is
conditional, does it hold the buff that grants it" in two places. The
plain-school path was migrated to C_UnitAuras.GetAuraDataBySpellName -- one
by-name lookup across the unit's auras. The split-damage path was not, and was
still walking 32 buff slots calling C_Spell.GetSpellName on each to compare the
name back, twice over, once for the initial school and once for the DoT's.

Both copies were the same twenty lines with the variable names changed, so they
fold into a SchoolImmune(unitId, school, targetName) helper that the split path
calls twice. Same answer, same order of checks: a permanent entry is immune, a
table entry without a buff is immune, a table entry with one is immune only
while the aura is up.

The plain-school path keeps its own inline version -- it is not the same
predicate. It gates on the recorded spell name first for the "unknown" school,
and a table entry carrying neither buff nor spell falls through to false there
where the split path calls it immune. Unifying those is a behavior change, not a
refactor, so it is left alone.

Utility.lua

@@ -8391,6 +8391,20 @@ local function ParseAfflictedCombatLog()
     end
 end
 
+-- True if the recorded immunity data makes `targetName` immune to `school` right
+-- now: outright when the entry is permanent, or only while it holds the buff the
+-- entry names. The buff test is one by-name lookup across the unit's auras via
+-- C_UnitAuras -- no slot scan, and it finds the aura wherever it sits.
+local function SchoolImmune(unitId, school, targetName)
+    local schoolData = school and CleveRoids_ImmunityData[school]
+    local data = schoolData and schoolData[targetName]
+    if not data then return false end
+    if data == true then return true end
+    if type(data) ~= "table" then return false end
+    if not data.buff then return true end
+    return CleveRoids.ClassicAPI.GetAuraDataBySpellName(unitId, data.buff, "HELPFUL") and true or false
+end
+
 -- Check if a unit is immune to a spell, damage school, or CC type
 -- Supports: CheckImmunity(unitId, "Flame Shock") or CheckImmunity(unitId, "fire") or CheckImmunity(unitId, "stun")
 function CleveRoids.CheckImmunity(unitId, spellOrSchool)
@@ -8487,53 +8501,10 @@ function CleveRoids.CheckImmunity(unitId, spellOrSchool)
             local initialSchool = splitData.initial
             local debuffSchool = splitData.debuff
 
-            -- Check initial school immunity (e.g., physical for Rake's initial hit)
-            local initialImmune = false
-            if initialSchool and CleveRoids_ImmunityData[initialSchool] then
-                local initialImmunityData = CleveRoids_ImmunityData[initialSchool][targetName]
-                if initialImmunityData == true then
-                    initialImmune = true
-                elseif type(initialImmunityData) == "table" and not initialImmunityData.buff then
-                    initialImmune = true
-                elseif type(initialImmunityData) == "table" and initialImmunityData.buff then
-                    -- Check if target has the immunity-granting buff
-                    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 == initialImmunityData.buff then
-                                initialImmune = true
-                                break
-                            end
-                        end
-                    end
-                end
-            end
-
-            -- Check debuff school immunity (e.g., bleed for Rake's DoT)
-            local debuffImmune = false
-            if debuffSchool and CleveRoids_ImmunityData[debuffSchool] then
-                local debuffImmunityData = CleveRoids_ImmunityData[debuffSchool][targetName]
-                if debuffImmunityData == true then
-                    debuffImmune = true
-                elseif type(debuffImmunityData) == "table" and not debuffImmunityData.buff then
-                    debuffImmune = true
-                elseif type(debuffImmunityData) == "table" and debuffImmunityData.buff then
-                    -- Check if target has the immunity-granting buff
-                    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 == debuffImmunityData.buff then
-                                debuffImmune = true
-                                break
-                            end
-                        end
-                    end
-                end
-            end
+            -- Initial school (e.g. physical for Rake's opening hit), then the DoT's
+            -- school (e.g. bleed). Immunity to either component skips the spell.
+            local initialImmune = SchoolImmune(unitId, initialSchool, targetName)
+            local debuffImmune = SchoolImmune(unitId, debuffSchool, targetName)
 
             -- Return true if immune to EITHER component
             if initialImmune or debuffImmune then