aacs: full-ladder resolve_candidate + correct mk_from_dk

resolve_candidate(candidate, mkb, unit_key_ro, vid) -> ResolvedChain: one
composed, PURE-DERIVATION boil-down for a candidate key at any ladder rung
(KeyCandidate::{Uk,Vuk,Mk,Pk,Dk}, each carrying the module's newtype). Walks
DK/PK/MK/VUK -> terminal unit keys, parsing Unit_Key_RO.inf at the version
the disc's MKB declares, and returns every CPS unit key as (cps_unit, key)
(matching ResolvedKeys) plus the intermediate chain. No sampling/validation
(that's the caller's unit_key_validates) and no position recovery (Dk is a
positioned DeviceKey; recover_dk_position first). Adds ProcessingKey newtype.
Consumers stop re-composing the ladder; every client hardens one impl.

Correct mk_from_dk: real Subset-Difference walk (derive_media_key_and_pk_from_dk)
instead of the Media-Key-Variant path, which needed integrator KCD absent
in-tree and Err'd for every real disc -- dead for both consumers. Drops the
now-unused vid arg.

src/aacs/mod.rs

@@ -36,7 +36,10 @@ pub const PATH_CONTENT_CERT: &str = "/AACS/Content000.cer";
 pub const PATH_CONTENT_CERT_ALT: &str = "/AACS/Content001.cer";
 
 // Boil-down derivation primitives (thin newtypes + wrappers over the crypto).
-pub use boil::{MediaKey, UnitKey, Vid, Vuk, mk_from_dk, mk_from_pk, uk_from_vuk, vuk_from_mk};
+pub use boil::{
+    KeyCandidate, MediaKey, ProcessingKey, ResolvedChain, UnitKey, Vid, Vuk, mk_from_dk,
+    mk_from_pk, resolve_candidate, uk_from_vuk, vuk_from_mk,
+};
 // Structured, English-free resolution trace.
 pub use trace::{KeyNode, KeyOutcome, KeyStep, ResolutionTrace, UnlockOutcome, UnlockStep};