fn to_limbs_field_vec<E: From<F>, F: Field>(x: &BigUint) -> Vec<E> {
        Self::to_limbs(x).into_iter().map(|x| F::from_canonical_u8(x).into()).collect::<Vec<_>>()
    }
Convert a BigUint to a Vec of F limbs (with len NB_LIMBS).
crates/curves/src/params.rs