ci: vitest workspaces

[kanadgupta]

🧰 Changes

Important

this continues to be a vitest supremacy account 😤

In this repo, we have tests that use process.chdir(), so we maintain a separate Vitest config for running those via a forks pool vs. the standard threads pool — see #870 for more background on this.

We've used two separate npm scripts (i.e., npm run test:multi && npm run test:single) to run our tests sequentially. I discovered this morning that Vitest's workspaces feature isn't just for monorepos — it's actually the recommended way to maintain multiple test configurations no matter the context.

In this PR, I consolidated our two test configs into a single workspace config. We get a few nice benefits by leveraging workspaces:

• No longer needing to manually pass in the correct config file when running certain test files (e.g., npx vitest --config vitest.single-threaded.config.ts [file]). In other words, npx vitest [file] ✨ just works ✨, which should make it a lot easier for new contributors to run tests
• Much cleaner test output — we now can see coverage across all files, rather than two separate coverage reports¹
• Easier to share options between the two configs
• A single config file to rule them all
• Tests seem to be faster (but hard to say)

🧬 QA & Testing

Do all the tests run? And do they still run and pass properly? Here's the latest test run in next for comparison: https://github.com/readmeio/rdme/actions/runs/8910638856

Footnotes

1. Small downside to this — workspaces don't allow you to configure coverage options. Not a huge deal since our coverage is great in this repo and we can stick to the defaults and it still addresses our needs. ↩