Block keyboard input during execution of boot.py on non-usb boards

[bill88t]

On usb boards it's not possible to interfere with boot.py since usb doesn't start up that early.
However on non-usb boards it's very much possible to do so.

This however makes it possible for serial noise (from plugging the board in) to send a KeyboardInterrupt and stop it.

I think it would eventually be a good idea to outright block all input while boot.py is running.

[bill88t]

This should also perhaps extend to safemode.py.

It's pretty much the boot.py of safe mode.
Having it be interrupted by a random serial interrupt, leaving the app stopped on a crashed headless board doesn't sound all that fun.

[tannewt]

My intention is that workflows start after boot.py is run but I think you are right that UART starts earlier.