RFC on rp2 project code and optimization possiblities

[samveen]

pico-mpy-2fa-totp contains code for the Pico W which I've forked and modified (and I've been using this as my primary TOTP device driver).

As this is my first successfully completed embedded project, I would greatly appreciate anyone with the time and inclination who'd take a quick look (a long hard look works too) at the code and point out any improvements that I should implement.