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/database/key_value/rooms/threads.rs

@@ -52,13 +52,13 @@ impl service::rooms::threads::Data for KeyValueDatabase {
             .collect::<Vec<_>>()
             .join(&[0xff][..]);
 
-        self.threadid_userids.insert(&root_id, &users)?;
+        self.threadid_userids.insert(root_id, &users)?;
 
         Ok(())
     }
 
     fn get_participants(&self, root_id: &[u8]) -> Result<Option<Vec<OwnedUserId>>> {
-        if let Some(users) = self.threadid_userids.get(&root_id)? {
+        if let Some(users) = self.threadid_userids.get(root_id)? {
             Ok(Some(
                 users
                     .split(|b| *b == 0xff)