Feature: Speed up tests with more caching

[etrepum]

I think we can improve the speed of the tests by tweaking our scripts and workflows. Here are some things I'd like to try:

• Have the builds be distinct jobs that caches the build artifacts that other jobs depend on. Maybe still do a matrix with os and node versions just to be safe?
• test-* jobs should use the cached build results so we are not running prepare-ci so much
• Consider inverting the relationship between dev and prod with e2e tests. Full matrix for prod, and a few runners to sanity check dev. Seems like that should run a little faster? It'll do fewer runtime sanity checks, but I think those are more for logic bugs rather than browser bugs