pub fn expand_key<const N: usize>(key: &[u8]) -> [[u8; 16]; N]Expand description
Expand a key into AES round keys (FIPS 197 §5.2).
N = 11-> AES-128 (Nk=4, Nr=10, 44 words -> 11 round keys)N = 15-> AES-256 (Nk=8, Nr=14, 60 words -> 15 round keys)
The schedule is computed with a constant-time S-box (no table lookups).