Migrate type tests from ts-expect to vitest built-in framework

[lihbr]

Is your feature request related to a problem? Please describe.

N/A, maintenance

Describe the solution you'd like

Vitest now provides a built-in framework to perform type testing: https://vitest.dev/guide/testing-types.html
Migrating our type tests to it could allow us to have both unit and type tests be powered by the same test framework. Vitest type testing also has a built-in way of naming type tests, making for a better DX.

Describe alternatives you've considered

Doing nothing and remaining on ts-expect is an option, although I think the better DX offered by Vitest type testing makes the move worth it. It also removes one library from our stack.

Additional context

I was pretty sure the new type testing feature of Vite was flagged as experimental, but I can't find any mention of it anymore in the doc/code, so I guess it's now considered stable.