Function hash_to_quintic_extension 

pub fn hash_to_quintic_extension(input: &[Fp]) -> Fp5

Hash an arbitrary-length input into the quintic extension Fp5.

Squeezes 5 field elements and packs them into an Fp5 limb-wise. Used by the Lighter Schnorr binding to derive a curve scalar from a message digest.

5 <= RATE, so the squeeze never re-permutes and there is no reason to allocate a Vec.