aacs: extract crypto.rs (shared AES primitives + constants)

Relocate the shared low-level primitives into a single crypto module:
aes_ecb_encrypt/decrypt, aes_cbc_decrypt, aes_g (from content/variant) and
aesg3 + AESG3_SEED (from keys), plus AACS_IV. Fixes the scatter where AES-G
lived in the 2.1 file and AES-G3 in keys. Relocation only — no rename, no
logic change (logic-hash identical to baseline; 277 items; 2210 tests green).

src/disc/mod.rs

@@ -5220,7 +5220,8 @@ mod tests {
     /// unit algorithm — ECB-derive the per-unit key, then AES-CBC encrypt the
     /// body with the fixed AACS IV.
     fn encrypt_unit_for_test(clear: &[u8], uk: &[u8; 16]) -> Vec<u8> {
-        use crate::aacs::content::{AACS_IV, ALIGNED_UNIT_LEN};
+        use crate::aacs::content::ALIGNED_UNIT_LEN;
+        use crate::aacs::crypto::AACS_IV;
         use aes::Aes128;
         use aes::cipher::{BlockEncrypt, KeyInit, generic_array::GenericArray};
         let mut unit = clear[..ALIGNED_UNIT_LEN].to_vec();