DP transform: make "guard $ not $ Q.isStrictSuffixOf r' $ lhs u" on/offable

it might be interesting to control this optimisation.

but then it may be not, because it has zero cost, so there's no reason to not do it?

OTOH it's low cost to implement the switch, just add a Boolean to https://gitlab.imn.htwk-leipzig.de/waldmann/pure-matchbox/-/blob/master/src/Matchbox/DP/Transform.hs#L27

data Config c  = DP { tracing :: Bool }