Fix ignoring optional deps when namespaced deps are used.

[xStrom]

Thanks for making cargo-hack!

I've been lately incorporating it into the Linebender CI that we use across a bunch of projects. Its --workspace and --each-feature functionalities have been especially useful.

When I was trying out the new CI script for our Kurbo project I found that cargo-hack does not handle Kurbo's optional dependecies (e.g. libm) correctly. That is with --optional-deps and even with --features libm. Upon looking closer I identified that cargo-hack is not behaving correctly because Kurbo makes use of namespaced dependencies.

In this PR I redesigned the namespaced_features test to be more comprehensive and better match what Cargo does.

The old test incorrectly stated:

When namespace dependency is used, other optional dependencies are also not treated as implicit features.

Cargo does not treat optional dependencies as implicit features only when that specific dependency has been referenced with the dep: prefix in an explicit feature. All other optional dependencies remain implicit features as before.

The actual code changes to get the test to pass were luckily minimal.

[taiki-e]

Thanks!

[taiki-e]

Published in v0.6.23.