Add real-world testing stage

[fredemmott]

This should probably:

1. clone the latest release of the HSL
2. install dependencies
3. run the typechecker
4. install dependencies

This shouldn't prevent a release being published, but should notify us somehow that new releases are needed. This covers the autoloader, HSL, hacktest, hh-clilib etc.

Releases (even nightlies) should be published so that they're installable to debug/test if needed.