`PidfdChildWatcher` based on [pidfd_open](https://www.man7.org/linux/man-pages//man2/pidfd_open.2.html) is the best child watcher implementation for Linux as it avoids race conditions and is most reliable of all of them. It requires Linux 5.3+ so this will be detected at runtime if it can be used and if so use this instead of `ThreadedChildWatcher`. `asyncio` will favor using `PidfdChildWatcher` over `ThreadedChildWatcher` in 3.12+ on systems which supports it.