GitLab

They do quite a lot of work, including setting up a type system,
generating Go code, and building it.

This package is by far the slowest to test. On a warm cache, 'go test
-count=1 ./...' shows all packages under 0.2s, while this one sits at
~1.5s.

1.5s is not unreasonable with a warm cache, but we can bring that down
to 0.6s on my quad-core laptop by just making all tests parallel. Note
that sub-tests aren't parallel for now, since there are multiple layers
of them and I'm not sure I even follow what's going on.

Mac is also disabled for the time being, since it seems to time out too
often.