Thinking about naming, it might be better to use TwitterAPIClient

[hppRC]

pub struct TwitterClient {}

↓

pub struct TwitterAPIClient {}

[hppRC]

example

before

let client = TwitterClient::new()

after

let api = TwitterAPIClient::new()

[hppRC]

Now

let api = kuon::TwitterAPI::new(...).await?;

kuon::TwitterAPI::new() is an async function because the API for obtaining the bearer token is called when the instance is created.