Refactor tests to use vercel dev

[de-luca]

Hi!

As evoked in #31, the tests seamed outdated.
I refactored them into using vercel dev.

This mainly remove the publication requirement.
However it seems like vercel dev cannot be used without linking to a project (see vercel/vercel#4925).

I kept what was beeing tested and only changed the way around.

This can also run on GitHub Actions, although it would require a vercel token.
(This can be seen here: https://github.com/de-luca/now-rust/actions?query=branch%3Agh)

[mike-engel]

@de-luca Thanks for this, and sorry for the delay. One comment, and could you rebase this with the latest master? Thanks!

[mike-engel]

This file can probably be deleted, no? Or is there a reason a file with a .backup extension is included?

[de-luca]

Good catch it was leftover from my tests.

[de-luca]

I rebased the branch and cleaned the leftover (I hope I didn't took too long).
Tests are passing with #25 additions.

[mike-engel]

Hi @de-luca, no worries at all! I've been busy as well. It looks like there's one last remaining conflict in the package-log.json file. When you have time to take a look at that, I think this looks good to merge thereafter.

[mike-engel]

Thanks for this @de-luca and for your patience 😄