Drop cpio-rs, replace with vendored code

[dralley]

This is necessary because RPM uses a modified CPIO format to support
>4gb file sizes. To maximize similarity and avoid producing nonsensical
RPM payloads, we should do the same.

closes #108

📜 Checklist

• Commits are cleanly separated and have useful messages
• A changelog entry or entries has been added to CHANGELOG.md
• Documentation is thorough
• Test coverage is excellent and passes
• Works when tests are run --all-features enabled

[drahnr]

Could you outline the exact differences/changes required to make the existing CPIO work?

[dralley]

@drahnr I outline it in #108

[dralley]

Note to self: make sure we handle the edge cases discussed here: https://blog.colindou.ch/posts/lets-make-an-os-cpio-weirdness/

That is: be careful with directories, and be careful with absolute paths. Extracting a cpio shouldn't automatically overwrite /usr/bin/blah.