The CSS (DVD-Video) bus-auth unlocker as a first-class external plugin, peer
to freemkv-unlock-ld. CssUnlocker impls libfreemkv::Unlocker — matches
DiscKind::Css, self-guards against the hardware (refuses NotApplicable without
issuing a CSS CDB if the drive reports a non-DVD profile), then runs the
libfreemkv bus-auth primitive (unlock_css_reads). libfreemkv keeps the bus-auth
+ keyless descramble; this crate owns the unlocker impl. Additive: a consuming
binary opts in with one register_unlocker(CssUnlocker::new()) line; the in-tree
built-in stays until clients are rewired.
