With every external caller of libdebuff:UnitDebuff / :UnitOwnDebuff
now on C_UnitAuras, the two public per-aura readers and the
nameplate-side cache they were feeding have no consumers.
- libs/libdebuff.lua: removes libdebuff:UnitDebuff (~120 lines),
libdebuff:UnitOwnDebuff (~75 lines), the _ownDebuffSortFunc helper,
and the local cache table. The slotOwnership / ownDebuffs /
allAuraCasts / pendingCasts bookkeeping stays — GetBestAuraCast
(libpredict) and GetEnhancedDebuffs (CleveRoids) still read it, and
the event handlers maintain it. GetSlotCaster / GetDebuffSlotMap
stay too; the DEBUFF_ADDED_OTHER handler and the debug printer use
them. File goes 2010 → 1870 lines.
- modules/nameplates.lua: deletes PlateCacheDebuffs (was already
rewritten on C_UnitAuras and unused once the display loop bypassed
the cache), PlateUnitDebuff, the cachedVerify scaffolding, and the
nameplate.UnitDebuff / nameplate.CacheDebuffs registrations.
- api/config.lua + modules/gui.lua: drops the now-defunct
"guessdebuffs" knob — its only effect was gating the dead cache.