Don’t loop 65536 FDs, trying to close them, when fork+exec:ing

All FDs should now have the CLOEXEC flag set, and thus there’s no
longer needed to manually loop “all” possible FDs and (trying to)
close them.

Note: the alsa module (alsalib, actually) is “racy” - while booting
up, it temporarily opens the asoundrc file without CLOEXEC. If
e.g. the script module starts its script inside this window, it’ll
have a leaked FD. Not much we can do about it though :/

Closes #169

CHANGELOG.md

@@ -34,6 +34,9 @@
 * i3: fixed “missing workspace indicator” (_err: modules/i3.c:94:
   workspace reply/event without 'name' and/or 'output', and/or 'focus'
   properties_).
+* Slow/laggy behavior when quickly spawning many `on-click` handlers,
+  e.g. when handling mouse wheel events
+  (https://codeberg.org/dnkl/yambar/issues/169).
 
 
 ### Security