refactor - Faucet: clean up faucet API & pow utils

[jurevans]

This PR is to clean up the utils & return types used in Faucet app. We can add any other improvements here as well.

[mateuszjasiuk]

LGTM!

[emccorson]

Looks good to me and the code looks much cleaner! I just left a couple of minor comments.

[emccorson]

Not sure if it matters, but I think this can still return a resolved Promise<undefined> even though the methods that use this return Promise<ChallengeResponse> etc.

[emccorson]

Actually, I was trying to figure out why TypeScript doesn't catch that. I'm not 100% sure, but if you add a return type to the then callback, it will catch it:

return (await fetch(new URL(`${this.url}${endpoint}`), {
  ...options,                                           
})                                                      
  .then((response): Promise<T> => {

TS2322: Type 'Promise<T> | undefined' is not assignable to type 'Promise<T>'.
Type 'undefined' is not assignable to type 'Promise<T>'.

[jurevans]

Thanks! I'll take a look. I think in the case it can return undefined, we should throw an exception so it can be caught in the app. I wanted to remove any case of undefined as it's very tedious

[jurevans]

I added a type for that error response, with { message, code }, so a correctly parsed error should always be this type, and in the case of undefined (if it can't get the reader and parse the error response) it will instead throw an error