AACS 2.0 full pipeline: handshake, bus key, decrypt, transparent API

- aacs.rs: content decryption (AES-CBC aligned units, bus decrypt, VUK
 derivation, unit key decrypt). 11 tests including synthetic roundtrip.
- aacs_handshake.rs: SCSI authentication (ECDH on AACS 160-bit curve,
 ECDSA sign/verify, AES-CMAC, bus key derivation, read_data_key).
 14 tests including EC order, ECDH shared secret, cert verification.
- disc.rs: transparent API — Disc::scan() detects AACS, authenticates,
 derives keys internally. ContentReader decrypts on the fly. App never
 sees AACS details.
- error.rs: AacsError (E7000) variant

BF v12 complete: 284 unique matches from 8 AWS instances.

Cargo.toml

@@ -15,6 +15,11 @@ sha1 = "0.10"
 aes = "0.8"
 cbc = "0.1"
 flate2 = "1"
+num-bigint = "0.4"
+num-traits = "0.2"
+num-integer = "0.1"
+rand = "0.8"
+cmac = "0.7"
 zip = { version = "2", default-features = false, features = ["deflate"] }
 
 [target.'cfg(target_os = "linux")'.dependencies]