Possible PR: `ps_is_alive()`

[dansmith01]

I'm adding a ps_is_alive() for my own package, and was wondering if you'd consider a PR here.

It caught me by surprise when ps_is_running() returned FALSE for a sleeping process on Linux. I know now that this is documented and expected behavior, but it still left me needing a way to determine if a process was in any of the alive states described by ps_status().

ps_is_alive <- function(p = ps_handle()) {
  assert_ps_handle(p)
  alive <- c("idle", "running", "sleeping", "disk_sleep", "uninterruptible", "waking")
  isTRUE(try(silent = TRUE, ps_status(p) %in% alive))
}

[dansmith01]

Actually, I'm mistaken. ps_is_running() will return TRUE for sleeping processes on Linux. I think there's something odd going on with ps_handles regenerated from a ps_string. Looking into it now...