chore: Bump @napi-rs/cli to 2.18.4

[Xanewok]

The 2.18.4 also contains the missing declare attribute when exporting but I didn't pull that in to reduce churn across our feature branches; I assume that all of them modifies the index.d.ts substantially and so let's do that separately at our leisure.

Can you expand on this? How valuable is to do that change? And, if you think it's valuable enough, could you open an issue about that?

Originally posted by @fvictorio in #617 (review)

As part of the maintenance work, we should bump the @napi-rs/cli crate to the newest version. The 2.18.4 version adds a declare annotation to the typings which is slightly more correct, as the generated index.d.ts does not define the exported types in 99% of the cases but only provides the typings for items already defined by the native addon.

I'm not sure whether the declare is still considered to be good practice but it certainly doesn't hurt for now. See https://www.typescriptlang.org/docs/handbook/declaration-files/by-example.html for some examples.