Enforce authentication statically for ListenBrainz client

[InputUsername]

We can use the "typestate pattern" to enforce authentication at compile time. To do this, we can make the ListenBrainz type generic over authentication status using a marker trait (eg. AuthStatus). A ListenBrainz<NotAuthenticated> instance then first has to be authenticated to obtain a ListenBrainz<Authenticated>, which can perform methods that require authentication.

I've implemented a proof-of-concept of this in the feature/static-auth branch.

Thoughts?

[shymega]

I really like this approach. Would you like me to rebase the branch against mainline?

Thinking of using the same approach for my Rust crate for Starling Bank.

[InputUsername]

Would you like me to rebase the branch against mainline?

Sure, go ahead. I'm very busy at the moment but I might have time to look into it soon.