(refactor): migrate all tests and test helper code to TS

[agilgur5]

• woot, all TS now!

  • get that big blue line for language TS on GitHub haha

• for the most part, not much more to do other than .js -> .ts

  • for the utils had to add some types around

• also use ESM instead of CJS in tests and test helpers

  • require -> import
  • module.exports -> export
  • the indentation change here with utils/fixture made git treat it as a delete + new instead of a rename

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This was, of course, done because #627 added lots of tests, and definitely not because TSDX became majority JavaScript after #627. This was definitely not because the majority JavaScript made TSDX classified as a "JavaScript" library

(it actually wasn't, I always wanted to convert the tests to TS, especially after the addition of the grep helper with JSDoc types in #525 (later moved to #627 which got merged first). but I can't say that didn't increase priority 😉 ).

[agilgur5]

That's better. Although I still don't think it's totally accurate