[depends] TypeScript

```bash
npm i --save-dev typescript @types/node tsx
```

🗞️ Newsflash: [ts-node is
dead](TypeStrong/ts-node#2073 (comment)).
(Indeed I had ample opportunity to confirm by myself that `ts-node`,
`ts-mocha` et al hardly work at all with modern Node, what with the
latter “helpfully” trying to parse the TypeScript by themselves, and
failing miserably when you try to import a type.)

Author: Dominique Quatravaux