refactor: switch to split cjs and esm builds and fully build with tsup

[favna]

I asked about this before in the server and I figured I'd just try it out, create a PR, and hear your thoughts on whether we merge this or not.

Zip of the new dist folder after running prepack:

new-dist.zip

---

Are the types wrong report before:

🎭 Import resolved to a CommonJS type declaration file, but an ESM JavaScript file. https://github.com/arethetypeswrong/arethetypeswrong.github.io/blob/main/docs/problems/FalseCJS.md

🐛 Import resolved to types through a conditional package.json export, but only after failing to resolve through an earlier condition. This behavior is a TypeScript bug (https://github.com/microsoft/TypeScript/issues/50762). It may misrepresent the runtime behavior of this import and should not be relied upon. https://github.com/arethetypeswrong/arethetypeswrong.github.io/blob/main/docs/problems/FallbackCondition.md


┌───────────────────┬────────────────────────────┐
│                   │ "@sapphire/framework"      │
├───────────────────┼────────────────────────────┤
│ node10            │ 🟢                         │
├───────────────────┼────────────────────────────┤
│ node16 (from CJS) │ 🟢 (CJS)                   │
├───────────────────┼────────────────────────────┤
│ node16 (from ESM) │ 🎭 Masquerading as CJS     │
│                   │ 🐛 Used fallback condition │
├───────────────────┼────────────────────────────┤
│ bundler           │ 🐛 Used fallback condition │
└───────────────────┴────────────────────────────┘

Are the types wrong report after:

 No problems found 🌟


┌───────────────────┬───────────────────────┐
│                   │ "@sapphire/framework" │
├───────────────────┼───────────────────────┤
│ node10            │ 🟢                    │
├───────────────────┼───────────────────────┤
│ node16 (from CJS) │ 🟢 (CJS)              │
├───────────────────┼───────────────────────┤
│ node16 (from ESM) │ 🟢 (ESM)              │
├───────────────────┼───────────────────────┤
│ bundler           │ 🟢                    │
└───────────────────┴───────────────────────┘