Add Test runs to CI, don't run `gh-pages` from forks

[oldwomanjosiah]

Skipping the usual PR template, since this is just CI

Changes

• Use matrix for builds, so that they can be done in parallel
• Add test workflow, using nextest to run all tests in repo
• Update formatting in all workflow files to follow yaml best practice
• Skip documentation workflow when dispatched on a fork

[oldwomanjosiah]

Related to this, but not really in scope: It might be worth it to run the CI in a container image with the deps already installed so that we don't have to re-install them every time.

https://docs.github.com/en/actions/using-jobs/running-jobs-in-a-container

[oldwomanjosiah]

This is pretty old, and definitely outdated.

[w-lfchen]

i'll see whether i can pick up the ideas of this pr at some point if that's fine

[oldwomanjosiah]

Yeah for sure! I don't run Linux as my daily right now so I can't really contribute there, but I'd love to see it get in fs