Add @types/leb128

[remcohaszing]

There’s no need anymore to use @ts-expect-error for the leb128 import, or to cast the types its functions return.

[wooorm]

Thanks for the types but it’s just a little script that I saved here for future reference for when Node supports WASM I can actually implement it. It doesn’t run.
Not sure if leb128 is needed then. It seems useful but also not maintained? 🤷‍♂️

Feels a bit weird to add dev-dependencies that aren’t used?

[wooorm]

Oh I guess TS still checks it all?

[remcohaszing]

Technically you could use @types/leb128, but not leb128 if it’s just for TypeScript. Personally I would keep it, as it’s needed to run a script that is part of this repo.