use async fn and return-position impl Trait in trait

[Emilgardis]

in 1.75 AFIT and RPITIT are stabilized, is there anything that needs this or would benefit from it?

[Nerixyz]

I suppose Client::req could use this:

twitch_api/src/client.rs

Lines 174 to 179 in f7168f4

	pub trait Client: Send + Sync {
	/// Error returned by the client
	type Error: Error + Send + Sync + 'static;
	/// Send a request
	fn req(&self, request: Request) -> BoxedFuture<'_, Result<Response, <Self as Client>::Error>>;
	}

Basically most things that box stuff? Though some depend on other libraries.