Test compilation under different feature flags on CI

[niklaslong]

As illustrated by #1685, our CI can currently miss breakage in feature-gated logic. We should be testing the succesful compilation under all feature flags on CI.

We could use cargo hack, though we'd need to adjust some of the settings as compiling without the defaults will break, as will the metrics crate with all features enabled (mutually exclusive features).

[raychu86]

@niklaslong @ljedrz Is this still relevant?

[ljedrz]

I don't think it's anything pressing, as I don't recall this being an issue in a long time, we're not frequently changing features, and we have CI runs for the combinations of features that we want to support. That being said, if we do run into something like that, we should remember tools like cargo hack.

[vicsn]

Closing this, but putting cargo hack on the list of repo maintenance tools to look into