bootsmith-core: the typed pipeline that turns an ISO + a target device into a sequence of write operations.
This crate is intentionally OS-agnostic. Concrete device I/O lives in
bootsmith-disk; ISO inspection in bootsmith-iso; boot-record bytes in
bootsmith-boot. The orchestration here calls into those via traits so the
pipeline can run against an in-memory Vec<u8> for unit tests just as
easily as against /dev/rdisk8.