lei: close inotify FD in forked child

lei: close inotify FD in forked child

Linux::Inotify2 2.3+ includes an ->fh method to give us the
ability to safely close an FD without hitting EBADF (and
automatically use FD_CLOEXEC).

We'll still need a new wrapper class (LI2Wrap) to handle it for
users of old versions, though.

Link: http://lists.schmorp.de/pipermail/perl/2021q3/thread.html