`slumber` process hangs at 100% CPU if parent process is killed

[LucasPickering]

If slumber's parent process is killed (with SIGTERM, although not sure it matters how), instead of terminating the slumber process hangs at 100% CPU and stops responding to SIGTERM itself. I've noticed this with both watchexec and zellij as the parent.

[LucasPickering]

I got pretty far on diagnosing this but couldn't figure out a fix. A few things I found out:

• Upgrading watchexec to 1.25.1 fixed the issue with watchexec (thanks to this PR)
• Zellij sends SIGHUP to its child process on quit, and that signal isn't being handled properly
• When the CPU goes to 100%, it's because it's stuck calling crossterm::poll
  • Despite giving a timeout, it never times out and just blocks on a read syscall
• The issue is related to some interaction between crossterm::poll and having signal_hook catch SIGHUP
  • If you remove SIGHUP from this list, or remove the poll call, the issue disappears and the process exits gracefully

I haven't figured out a way to reproduce this outside of zellij, so it's hard to submit a bug report anywhere for it. I'm not really sure if it's a bug in crossterm or signal_hook (or neither?).