[FEAT] OCI/GHCR Support

[Samueru-sama]

zsync is an amazing tool, but it lacks native support for OCI container images. Is it possible for it to work with OCI/GHCR?

[xplshn]

For a simple & readable implementation, I've implemented resumable OCI downloads in Go in 437LOC, you can see it here: https://github.com/xplshn/dbin/blob/master/fetch.go