Support for handling sha512-addressed repos in cfsctl and composefs-setup-root

[chaserhkj]

This PR changes cfsctl to use sha512-addressed composefs repo by default, this confronts to the behavior of bootc, making the two tools compatible with each other. An additional flag --use-sha256-object-id is also added to enable cfsctl to work with legacy repos.

kernel cmdline parse logic in composefs-setup-root is also changed, both sha256 and sha512 length addresses would be attempted before returning an error, improving robustness within initramfs.

Fixes #197

[Johan-Liebert1]

I had reviewed earlier, but forgot to press submit :|

[chaserhkj]

Sorry missed another cargo fmt that pulled in another CI failure. Just fixed. I'll just add cargo fmt as my git hook

[cgwalters]

So I'm OK with this, but I do think we should add the repo metadata at some point.

In practice...because we're not shipping this project even on crates.io (much less as a standalone package/component) making "breaking" changes like this doesn't matter much.

But...we do want to eventually do that I think in order to replace the composefs-c project. But when we do that there will probably be deeper changes anyways.

[cgwalters]

This also relates to the repo metadata thing. If we had that, then we would know precisely what sha digest length we should be expecting here.

[cgwalters]

So...this will increase compatibility with bootc when using the raw CLI, but it will also have the effect of changing the default here too, including AFAIK all CI jobs here. I think that's probably fine...but worth noting.

[cgwalters]

Most of the CI here was already broken for other reasons, but this creates a new problem:

++ cfsctl --repo /tmp/sysroot compute-id --bootable /mnt/base
error: one or more required arguments were not provided

I think it might be because it's missing default_value_t in the clap metadata?