[feature request] `waitpid` via `epoll()`

Currently the implementation `waitpid` is using spin waiting, which could lead to performance issues. It is possible to refactor it via `pidfd_open` and `epoll` to allow CPU to save battery. https://github.com/uutils/procps/blob/1194b3f7603d7e216202b74dc845ec44997354ad/src/uu/pidwait/src/wait.rs#L28