The AACS host-certificate bus-auth unlocker as a first-class external plugin,
peer to freemkv-unlock-ld and freemkv-unlock-css. AacsUnlocker impls
libfreemkv::Unlocker — matches DiscKind::Aacs, self-guards against the hardware
(refuses NotApplicable without issuing a handshake CDB if the drive reports a
non-Blu-ray profile), gathers host certs from the scan options, and runs the
libfreemkv cert-handshake primitive to learn the Volume ID + bus key. libfreemkv
keeps the handshake + AACS content decryption; this crate owns the unlocker.
Additive: a consuming binary opts in with one register_unlocker(...) line.
