Function mds_circulant_karatsuba_12 

pub fn mds_circulant_karatsuba_12<F: PrimeCharacteristicRing, A: Algebra<F> + Clone>(
    state: &mut [A; 12],
    col: &[F; 12],
)

Circulant matrix-vector multiply for width 12 via Karatsuba convolution.