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/extract.rs

@@ -1101,13 +1101,13 @@ mod tests {
         // Flag encrypted via CPI bits (byte 0) before key derivation.
         unit[0] |= 0xC0;
         let header: [u8; 16] = unit[..16].try_into().unwrap();
-        let derived = crate::aacs::content::aes_ecb_encrypt(unit_key, &header);
+        let derived = crate::aacs::crypto::aes_ecb_encrypt(unit_key, &header);
         let mut k = [0u8; 16];
         for i in 0..16 {
             k[i] = derived[i] ^ header[i];
         }
         let cipher = Aes128::new(GenericArray::from_slice(&k));
-        let mut prev = crate::aacs::content::AACS_IV;
+        let mut prev = crate::aacs::crypto::AACS_IV;
         let blocks = (crate::aacs::ALIGNED_UNIT_LEN - 16) / 16;
         for i in 0..blocks {
             let o = 16 + i * 16;

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();

src/disc/verify.rs

@@ -523,13 +523,13 @@ mod tests {
         use aes::cipher::{BlockEncrypt, KeyInit, generic_array::GenericArray};
         unit[0] |= 0xC0; // CPI flag => reads as encrypted
         let header: [u8; 16] = unit[..16].try_into().unwrap();
-        let derived = crate::aacs::content::aes_ecb_encrypt(unit_key, &header);
+        let derived = crate::aacs::crypto::aes_ecb_encrypt(unit_key, &header);
         let mut k = [0u8; 16];
         for i in 0..16 {
             k[i] = derived[i] ^ header[i];
         }
         let cipher = Aes128::new(GenericArray::from_slice(&k));
-        let mut prev = crate::aacs::content::AACS_IV;
+        let mut prev = crate::aacs::crypto::AACS_IV;
         for i in 0..(ALIGNED_UNIT_LEN - 16) / 16 {
             let off = 16 + i * 16;
             for j in 0..16 {