pub fn expand_s<P: Params>(
rho_prime: &[u8; 64],
) -> ([[i32; 256]; 7], [[i32; 256]; 8])Expand description
Expand the secret vectors s1 and s2 from a seed.
Implements Algorithm 33 of FIPS 204 (ExpandS). Generates the secret
vectors by calling rej_bounded_poly with incrementing nonces:
nonces 0..l for s1, and l..(l+k) for s2.
rho_prime: 64-byte secret seed derived during key generation.
Returns (s1, s2) where s1 has MAX_L polynomials (valid 0..l) and s2
has MAX_K polynomials (valid 0..k), each with coefficients in [-eta, eta].