Have cargo-msrv use cargo-like workspace inheritance

[foresterre]

Implement actual issue from #1023

The difficulty with doing this by default, i.e. when running cargo msrv verify from a workspace root, is that you'll have to disambiguate between "running verify against a root package" or "running verify against all workspace members plus the root package"

I would have imagined that it would inherit the behavior of cargo — use the default workspace members — which is the root if one exists, or all members if one doesn't exist or --workspace is passed.

(along with @eitsupi, I'm a dev of prql. I'm separately a maintainer of insta, where we do exactly that)

Thanks for the feedback!

I never realized that the following is the cargo default for a virtual workspace:

or all members if one doesn't exist

I agree that inheriting cargo's behavior is most logical.

Originally posted by @foresterre in https://github.com/foresterre/cargo-msrv/issues/1023#issuecomment-2405641894