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/utils/buffd/parser.rs

@@ -97,7 +97,7 @@ impl<'a, 'b> MsgParser<'a, 'b> {
 
     pub fn fd(&mut self) -> Result<Rc<OwnedFd>, MsgParserError> {
         match self.buf.get_fd() {
-            Ok(fd) => Ok(Rc::new(fd)),
+            Ok(fd) => Ok(fd),
             _ => Err(MsgParserError::MissingFd),
         }
     }