Function use_hint_vec 

pub fn use_hint_vec(
    h: &[[i32; 256]],
    r: &[[i32; 256]],
    gamma2: i32,
    len: usize,
) -> [[i32; 256]; 8]

Apply use_hint to every coefficient of a hint vector and an approximate vector.

Returns the corrected w1 vector used during verification.