 trivial empty traversal.
--
-- @'ignored' :: 'IndexedTraversal' i s s a b@
--
-- @'ignored' ≡ 'const' 'pure'@
ignored :: Applicative f => kafb -> s -> f s
ignored _ = pure
{-# INLINE ignore
ignored :: Applicative f => kafb -> s -> f s
ignored _ = pure
ignored _ = pure