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/xcon/formatter.rs

@@ -1,17 +1,17 @@
 use {
-    crate::xcon::Message,
+    crate::{utils::buf::DynamicBuf, xcon::Message},
     std::rc::Rc,
     uapi::{AssertPacked, OwnedFd, Packed},
 };
 
 pub struct Formatter<'a> {
     fds: &'a mut Vec<Rc<OwnedFd>>,
-    buf: &'a mut Vec<u8>,
+    buf: &'a mut DynamicBuf,
     ext_opcode: u8,
 }
 
 impl<'a> Formatter<'a> {
-    pub fn new(fds: &'a mut Vec<Rc<OwnedFd>>, buf: &'a mut Vec<u8>, ext_opcode: u8) -> Self {
+    pub fn new(fds: &'a mut Vec<Rc<OwnedFd>>, buf: &'a mut DynamicBuf, ext_opcode: u8) -> Self {
         Self {
             fds,
             buf,