consider using http::Uri dependency instead of url::Url

[DanGould]

The payjoin protocol deals with HTTP messages, not ftp/unix/data protocols and so using the lighter weight http::Uri type may be more appropriate than url::Url and give validation control over exactly the types of URLs that we need to deal with.

The original bip78 crate from Kixunil used url so we just kept with it without thinking through this dependency https://github.com/Kixunil/payjoin/blob/master/bip78/Cargo.toml