Migrate testing setup from Jest to Vitest

[RichDom2185]

We want to migrate to vitest, which has been designed as a drop in replacement for jest. I find that getting jest to work with the wide mix of ESM and CJS syntaxes has been a major headache, and configuration for jest has always been needlessly complicated.

vitest supports TypeScript and ESM out of the box and has generally provided a far smoother experience, especially when dealing with dependencies that need to be tested.