New port: sysutils/evhz: tool for measuring evdev event rate

A tool for measuring evdev event rate
(mouse polling rate, touchpad event rate, etc.)

Reported average is for the last 64 samples, or as many as we have so far.

WWW: https://gitlab.com/iankelling/evhz

PR: 239466
Submitted by: Greg V <greg@unrelenting.technology>