Function mds_circulant_karatsuba_16 

pub fn mds_circulant_karatsuba_16<F: PrimeCharacteristicRing, A: Algebra<F> + Clone>(
    state: &mut [A; 16],
    col: &[F; 16],
)

Circulant matrix-vector multiply for width 16 via Karatsuba convolution.