Make simple_request::Client generic to the executor

Part of https://github.com/serai-dex/serai/issues/682.

We don't remove the use of `tokio::sync::Mutex` now as `hyper` pulls in
`tokio::sync` anyways, so there's no point in replacing it. This doesn't yet
solve TLS for non-`tokio` `Client`s.

patches/simple-request/src/lib.rs

@@ -1,18 +1,2 @@
-pub use simple_request::{hyper, Error, Request, Response};
-
-#[derive(Clone, Debug)]
-pub struct Client(simple_request::Client);
-
-impl Client {
-  pub fn with_connection_pool() -> Client {
-    Self(simple_request::Client::with_connection_pool().unwrap())
-  }
-
-  pub fn without_connection_pool(host: &str) -> Result<Client, Error> {
-    simple_request::Client::without_connection_pool(host).map(Self)
-  }
-
-  pub async fn request<R: Into<Request>>(&self, request: R) -> Result<Response<'_>, Error> {
-    self.0.request(request).await
-  }
-}
+pub use simple_request::{hyper, Error, Request, TokioClient as Client};
+pub type Response<'a> = simple_request::Response<'a, hyper_util::rt::tokio::TokioExecutor>;