This brings io_uring helper methods to Zig for kernels >= 5.4.

We follow liburing's design decisions so that anyone who is comfortable with
liburing (https://unixism.net/loti/ref-liburing/index.html) will feel at home.

Thanks to @daurnimator for the first draft.

Refs: https://github.com/ziglang/zig/pull/3083
Signed-off-by: Joran Dirk Greef <joran@coil.com>