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/service/rooms/edus/presence/mod.rs

@@ -182,7 +182,7 @@ fn process_presence_timer(user_id: OwnedUserId) -> Result<()> {
         }
     }
 
-    let new_state = match (&presence_state, last_active_ago.map(|ago| u64::from(ago))) {
+    let new_state = match (&presence_state, last_active_ago.map(u64::from)) {
         (PresenceState::Online, Some(ago)) if ago >= idle_timeout => {
             Some(PresenceState::Unavailable)
         }