[FEATURE] support :run-while on deflisten

Description of the requested feature

Would be nice if you could toggle the deflisten script directly via yuck, instead of by e.g. making a file marker or some such. Nice for anything even remotely heavy, and just for peace of mind that you're not running it needlessly at all times.

Proposed configuration syntax

(defvar clicked false)

(deflisten mouse_pos
	:initial '{"X":"0","Y":"0","SCREEN":"0","WINDOW":"0"}'
	:run-while clicked
	'./get_mouse_pos.sh' ;; repeated polling
)

This will terminate the script when clicked is false and re-run the script when clicked becomes true again.

Additional context

No response