tar-split

This release notably drops go1.17 (due to dependencies that no longer support 1.17), and adds testing for go1.21 and go1.22.

Additionally adds a new function for iterating over only the headers of a the metadata. Previously this would have required assembling the full tar stream with is expensive for such an operation. Thanks @mtrmac

and thanks @testwill for the typo fix.

This is a bit of bringing tar-split up-to-date, but also this will be the last release to support up to go1.16. Some of the deps to be updated now only support go1.18 (kindof go1.17) and above. Here's looking at you golang.org/x/sys/unix ... 🙄