Use cargo_metadata to get manifest data (adds workspace inheritance support)

[oeb25]

This commit uses the cargo_metadata crate to derive information about the crate, as opposed to only parsing Cargo.toml.

In particular, this helps when fields in the manifest are inherited from the workspace, for example if version = { workspace = true }.

One thing cargo_metadata does not provide, is badges, so these are still parsed from Cargo.toml.

The error messages also changed as a result of propagating the errors from cargo_metadata, and thus some of the tests had to be altered.

[sshine]

This is great, thåmbs up! It is the better way of resolving:

• Workspace inheritance breaks cargo readme #81

I'd like to take bring it to the end goal.

Since it comes from oeb25:master, I can't push to it even if I were a co-maintainer here.

If you'd like, perhaps you can rebase this and I can see if I can start the CI build and review. If you're not interested, I will open another PR and cherry-pick your changes for attribution.

[webern]

Since it comes from oeb25:master, I can't push to it even if I were a co-maintainer here.

You might be able to? Maybe it involves using the gh command line tool? I've been able to push, force push, and rebase to contributor PR branches. I'm not sure how that works under the hood because surely I haven't actually changed the branch in that person's repo. Anyway, you can edit a PR, at least with gh, afaik.

[sshine]

There's a deliberate limitation on GitHub which prevents maintainers of the original repo from pushing to the forked master/main branch of a pull request. It has some kind of special status. Since the PR is quite old, the workaround might not be too bad.