The library no longer loads a keydb anywhere. The scan path always captures the
disc's AACS inputs (MKB, VID, Unit_Key_RO.inf) and resolves NO key; a caller
resolves a Key from a key source and applies it via Disc::decrypt_with.
- ScanOptions loses keydb_path / unit_key / disable_keydb (and the path search);
it now carries only optional DriveCredentials (host certs) for the live-drive
AACS handshake. do_handshake_cert uses those instead of loading the keydb.
An unlocked / LibreDrive drive takes the OEM Volume-ID path and needs none.
- The mux input() path takes caller-resolved unit_keys instead of a keydb_path,
and applies them via decrypt_with.
- Deleted the now-dead inline resolve_encryption / resolve_encryption_static.
All 700+ lib tests pass.