Support tarballs with the GNU Sparse File extension

[chshersh]

Currently, tool-sync can't support some tools because their macOS archives use the GNU Sparse File feature:

https://github.com/chshersh/tool-sync/blob/b79eeb91cfdc3a122e6693d503117f68ff1fb44e/src/sync/db.rs#L99-L110

This is blocked by the following issue in tar crate:

• https://github.com/alexcrichton/tar-rs/issues/295