io: use io_uring for all io

There should no longer be any

- read
- write
- connect
- sendmsg
- recvmsg
- accept

calls in the codebase. Previously we were using a mix of io_uring and
these calls which had some negative effects: Since we were using the old
system calls, we had to set the file descriptors to non-blocking. But
our io_uring code did not handle EAGAIN. This lead to programs sometimes
being killed when the wayland IO was actually blocking.

Now all file descriptors are set to blocking, but io_uring makes it
non-blocking from our perspective. The one exception are evdev files
because they are read via libinput and libinput uses the old system
calls.

src/io_uring/ops/poll.rs

@@ -32,6 +32,7 @@ impl IoUring {
         self.poll(fd, c::POLLIN).await.merge()
     }
 
+    #[allow(dead_code)]
     pub async fn writable(&self, fd: &Rc<OwnedFd>) -> Result<c::c_short, IoUringError> {
         self.poll(fd, c::POLLOUT).await.merge()
     }