Upgrade to support MicroPython 1.20.0

[Rory Allen]

Check ability to use MicroPython 1.20.0 to make use of the new bug fixes and potential ability to use threading more reliably, as well as features when using a Pico W

[Rory Allen]

A quick test of a custom compiled uf2 with the Dockerfile changed to use MicroPython 1.20.0 runs and seems to work properly on the hardware

[Chris I-B]

I opened a PR earlier today to address this: #272

I've noted the things I've been able to test so far, but it's not complete yet.

[Rory Allen]

Implemented in #272