Implement "Magic effect expired" event
ATM we execute effect-related logic in the Actors::calculateCreatureStatModifiers() every frame (bound items, summons, corprus, etc.), where we check if desired effect is present.
It would be nice to have the some kind "effect expired" event, where we can register logic which should be executed when spell effect expires (restore stats after corprus, remove bound item, remove summon, re-equip items after EXTRA_SPELL effect, etc.).