fix every clippy warning possible, remove io_uring as default feature

this project's codebase is so horrendous, im shocked that no one has ran
clippy at all. it had ~200 total lint warnings, some with performance
issues and unsoundness, and the rest just very ugly codebase. i have sat
down and fixed as many of these as possible and i am exhausted.
i haven't fixed some extremely complex ones, but i brought it down from
~200 to ~30.

i have also removed io_uring as a default feature due to it falling
under the same category as linux eBPF: major kernel attack surface for
minimal performance gains. this also makes it impossible to cross-compile
from macOS to Linux because io_uring does not exist in Darwin land.
there are far better ways to achieve better performance than io_uring on
the codebase level.

Signed-off-by: strawberry <june@girlboss.ceo>

src/api/client_server/session.rs

@@ -117,12 +117,10 @@ pub async fn login_route(body: Ruma<login::v3::Request>) -> Result<login::v3::Re
             } else {
                 return Err(Error::BadRequest(ErrorKind::Forbidden, "Bad login type."));
             };
-            let user_id =
-                UserId::parse_with_server_name(username, services().globals.server_name())
-                    .map_err(|_| {
-                        Error::BadRequest(ErrorKind::InvalidUsername, "Username is invalid.")
-                    })?;
-            user_id
+
+            UserId::parse_with_server_name(username, services().globals.server_name()).map_err(
+                |_| Error::BadRequest(ErrorKind::InvalidUsername, "Username is invalid."),
+            )?
         }
         _ => {
             warn!("Unsupported or unknown login type: {:?}", &body.login_info);
@@ -163,6 +161,7 @@ pub async fn login_route(body: Ruma<login::v3::Request>) -> Result<login::v3::Re
 
     info!("{} logged in", user_id);
 
+    #[allow(deprecated)]
     Ok(login::v3::Response {
         user_id,
         access_token: token,