Function forward_hessian_vec_prod

pub fn forward_hessian_vec_prod<const N: usize, F>(
    f: &'_ dyn Fn(&[F; N]) -> Result<[F; N], Error>,
) -> impl Fn(&[F; N], &[F; N]) -> Result<[F; N], Error> + '_
where
    F: Float + FromPrimitive,