touchy: pegs one CPU core via continuous X redraw traffic at idle

[grandixximo]

touchy pegs one core at idle. Measured under xvfb (uspace RIP, #4054 build):

• The pegged core is the X server (Xvfb 90-96%), not touchy's Python (touchy ~10% CPU, ~85% of py-spy samples idle in the GTK main loop).
• axis, gmoccapy, and qtdragon keep Xvfb near 0% under the same setup; only touchy floods X.
• So it is not a sleepless busy-loop; touchy generates continuous X redraw traffic, likely the periodic set_label widget updates in periodic_status/periodic_radiobuttons (src/emc/usr_intf/touchy/touchy.py).

Pinning the exact widget needs GTK draw-count instrumentation.