Function sample_shared_field_challenges 

pub fn sample_shared_field_challenges<C>(
    transcript: &mut impl Transcript,
    n: usize,
    q_star_cfg: &C,
    prime_cfgs: &[C],
) -> Vec<Vec<C::Element>>
where
    C: BaseFieldConfig,
    C::Integer: ConstTranscribable,

Sample n shared integer challenges in $[0, q^*)$ and return the result as a per-family matrix: outer length prime_cfgs.len(), inner length n. Entry [i][k] is the $k$-th shared integer typed in $F_{q_i}$.