Arduino-mbed core porting

[dogtopus]

This is specifically for the 32Mib ROM used on OwO. Regular Pico only has 16Mib and there's an Arduino variant that uses 128. Both don't fit OwO perfectly. It would be better to split the region as 3MiB for code and 1MiB as NVRAM for persistent states and keys, although using stock Arduino-mbed directly and have a 2MiB/2MiB cut is also acceptable.