Disc::decrypt_with now takes Device / Processing / Media / Volume keys in
addition to Unit. A caller hands in whatever level it resolved and the
library derives down the AACS chain to the per-CPS-unit keys, then
decrypts:
Device -> MKB walk -> media key -> VUK -> per-CPS unit keys
Processing -> MKB -> media key -> VUK -> per-CPS unit keys
Media -> Volume ID -> VUK -> per-CPS unit keys
Volume -> Unit_Key_RO.inf, one unit key per CPS unit
Unit -> used directly (terminal)
Derivation stays centralized in the version-dispatched resolver
(1.0 / 2.0 / 2.1), fed by a single-key provider built from the supplied
key — no new crypto. Volume notably does NOT stop at the volume key: it
decrypts every CPS unit's key.
Scan stashes the AACS inputs (Unit_Key_RO.inf and MKB) on AacsState so an
out-of-band decrypt_with can derive without re-reading the disc.
Non-breaking: Key is #[non_exhaustive] and the existing Unit path is
unchanged. New tests cover the Volume -> per-CPS derive-down, the
missing-inputs error, and the no-units rejection.
MattJackson
9012101573