add option to stay awake on usb; suppress debug logging

[projectgus]

FWIW after talking to tsd on IRC I implemented an NVS-optional version of this here: https://github.com/projectgus/micropython-esp32/commit/0f7bcb2f7b162fcf6caca390d85e90a1adccc984

I haven't sent a PR because it turned out to be not very useful for me, but it works - can send PR if desirable.