[Meta] Improve CI/CD

Would it make sense to parallelize the "test" stage next to the "build" stage (and have "deploy" stage dependent on the other two)? Won't make much difference for a while, but in theory? Also wonder whether "build" should be "build-docs" and "deploy" should be "deploy-docs" given we will eventually have other tasks that could probably be performed in parallel. I'm undoubtedly over-optimizing...