Port to oci-spec 0.7

[cgwalters]

Now we can use a proper Digest type.

[cgwalters]

CI here can't succeed on semver-incompat bumps, though what I could do is prep the PR for ostree-rs-ext in advance, and point CI at it temporarily

[jeckersb]

CI here can't succeed on semver-incompat bumps, though what I could do is prep the PR for ostree-rs-ext in advance, and point CI at it temporarily

Yeah I was just looking into that. Wrapping my head around the dependency graph of things in CI. I started on porting ostree-rs-ext over to ocidir 0.3.0 which if I'm following is required to untangle all of this.

[cgwalters]

@jeckersb this is ready now, I pointed CI at your branch in ostreedev/ostree-rs-ext#663

Then we can release this crate and change your PR to use the published crate, then when we publish ostree-rs-ext we can change this to reference the published version of that...