auras: scan through GetAuraSlots instead of by-index loops

Every aura scan loop (unit frame buffs/debuffs, dispel indicators, buff and
custom indicators, player buff frame, buffwatch bars, tooltip buff row) now
enumerates a unit's auras once with C_UnitAuras.GetAuraSlots and reads each
aura by slot id via the positional C_UnitAuras.UnitAuraBySlot. The by-index
getters re-walk the aura array from slot 0 on every call, so a per-button
loop over them was quadratic in the aura count; one enumeration plus a
by-slot read per aura is linear.

pfUI.api.ScanAuraSlots(unit, filter, buf, max) wraps GetAuraSlots' fill-a-
table form (table as the 5th argument) so no vararg Lua frame is involved:
Lua 5.0 allocates an `arg` table for every vararg call, which showed up as
nameplate OnUpdate/OnEvent memory growth in the first cut of this change.

Single by-index reads in tooltip and click handlers are unchanged (one call
each, and SetUnitAura takes the same index).

Requires the ClassicAPI build that adds GetAuraSlots' fill form; on an older
DLL the 5th argument is ignored and ScanAuraSlots would read the first slot
id as the count.

modules/buff.lua

@@ -7,6 +7,15 @@ pfUI:RegisterModule("buff", function ()
 
   local br, bg, bb, ba = GetStringColor(pfUI_config.appearance.border.color)
 
+  -- Player aura slot ids, enumerated once per refresh pass (ScanPlayerAuraSlots)
+  -- and read per button by its aura index: one GetAuraSlots walk per range
+  -- instead of a by-index walk per button.
+  local helpfulSlots, harmfulSlots = {}, {}
+  local function ScanPlayerAuraSlots()
+    ScanAuraSlots("player", "HELPFUL", helpfulSlots, 32)
+    ScanAuraSlots("player", "HARMFUL", harmfulSlots, 16)
+  end
+
   local function RefreshBuffButton(buff)
     if buff.btype == "HELPFUL" then
       if C.buffs.separateweapons == "1" then
@@ -23,7 +32,8 @@ pfUI:RegisterModule("buff", function ()
       CreateBackdropShadow(buff)
     end
 
-    local name, icon, count, dispelType, _, expirationTime, _, _, _, spellId = C_UnitAuras.UnitAura("player", buff.id, buff.btype)
+    local slots = buff.btype == "HELPFUL" and helpfulSlots or harmfulSlots
+    local name, icon, count, dispelType, _, expirationTime, _, _, _, spellId = C_UnitAuras.UnitAuraBySlot("player", slots[buff.id])
 
     --detect weapon buffs
     if buff.btype == "HELPFUL" and ((C.buffs.separateweapons == "0" and buff.gid <= pfUI.buff.wepbuffs.count) or (pfUI.buff.wepbuffs.count > 0 and buff.weapon ~= nil)) then
@@ -166,6 +176,8 @@ pfUI:RegisterModule("buff", function ()
       pfUI.buff.wepbuffs.count = 0
     end
 
+    ScanPlayerAuraSlots()
+
     for i=1,32 do
       RefreshBuffButton(pfUI.buff.buffs.buttons[i])
     end
@@ -246,6 +258,9 @@ pfUI:RegisterModule("buff", function ()
     end
   end)
 
+  -- CreateBuffButton refreshes each new button from the slot buffers
+  ScanPlayerAuraSlots()
+
   -- Weapon Buffs
   pfUI.buff.wepbuffs = CreateFrame("Frame", "pfWepBuffFrame", UIParent)
   pfUI.buff.wepbuffs.count = 0