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/buf_in.rs

@@ -15,7 +15,7 @@ pub struct BufFdIn {
     fd: Rc<OwnedFd>,
     ring: Rc<IoUring>,
 
-    in_fd: VecDeque<OwnedFd>,
+    in_fd: VecDeque<Rc<OwnedFd>>,
 
     in_buf: Buf,
     in_left: usize,
@@ -86,7 +86,7 @@ impl BufFdIn {
         Ok(())
     }
 
-    pub fn get_fd(&mut self) -> Result<OwnedFd, BufFdError> {
+    pub fn get_fd(&mut self) -> Result<Rc<OwnedFd>, BufFdError> {
         match self.in_fd.pop_front() {
             Some(f) => Ok(f),
             None => Err(BufFdError::NoFd),