Upgrade repo to modern tooling

[mattpocock]

• [ ] Upgrade TS to latest
• [ ] Upgrade to strict mode #567
• [ ] Move to vitest #571
• [ ] Move to tsup #570
• [ ] Add arethetypeswrong/cli #569
• [ ] Upgrade ESLint and migrate the config
• [ ] Upgrade prettier
• [ ] Get prettier to run on the tests directory #578
• [ ] Fail CI if repo is not properly formatted
• [ ] Remove eslint-config-prettier #579

[jessekrubin]

This may fit here w/ respect to modern-talk

Why does this library use namespaces (eg result.ts)? is it a legacy thing?