badger2040.system_speed regression

[Gadgetoid]

Since badger2040.system_speed was migrated into Python to use machine.freq it's lost a lot of edge cases that handle lower clock frequencies, and additionally lacks the slight overvoltage that may make higher frequencies stable on some systems.

We need a custom module giving an implementation of machine.freq that looks more like the old Badger 2040 system_speed function.

Old function: https://github.com/pimoroni/pimoroni-pico/blob/c8d3b6b7d1875b35147867e31b102ffcad128788/micropython/modules/badger2040/badger2040.cpp#L535-L591

New function: https://discord.com/channels/801944326401556512/801944538981466183/1110852447242567690

MicroPython's machine.freq(): https://github.com/micropython/micropython/blob/ed7a3b11d9a6c21a964d55ebfcdefeb392389d10/ports/rp2/modmachine.c#L102-L116