Function certify_isogeny 

pub fn certify_isogeny(
    domain: &Curve,
    kernel_gen: &Point,
    ell: u64,
    n: u64,
) -> Option<TorsionImageWitness>

Build a genuine certified witness: the real ell-isogeny with kernel ⟨kernel_gen⟩ on domain, together with the images of an actual E[n] basis (n coprime to ell, so φ is an isomorphism on the n-torsion). Its verify() passes by construction. None if the isogeny or basis cannot be formed.