No API to retrieve the schema type

[d3lm]

While using the Rust crate for ada-url I have noticed that there's only url.host_type() but there's no getter for the schema type. It'd be great if we could expose the schema type as well so we have the same API surface as the C++ lib.

For example:

let url = Url::parse(href, None).expect("bad url");
let schema_type = url.schema_type();