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/backends/metal/monitor.rs

@@ -213,11 +213,7 @@ impl MetalBackend {
                     return;
                 }
             };
-            if let Err(e) = set_nonblock(res.fd.raw()) {
-                log::error!("Could set drm fd to non-blocking: {}", ErrorFmt(e));
-                return;
-            }
-            let master = Rc::new(DrmMaster::new(res.fd.clone()));
+            let master = Rc::new(DrmMaster::new(&slf.state.ring, res.fd.clone()));
             let dev = match slf.create_drm_device(dev, &master) {
                 Ok(d) => d,
                 Err(e) => {