Function mds_circulant_karatsuba_8 

pub fn mds_circulant_karatsuba_8<F: PrimeCharacteristicRing, A: Algebra<F> + Clone>(
    state: &mut [A; 8],
    col: &[F; 8],
)

Circulant matrix-vector multiply for width 8 via Karatsuba convolution.