Support for fast printing

[MaddoScientisto]

I'm a game boy camera user and the Photo! custom ROM allows printing at higher speeds than what the printer normally supports, it supports several modes:

Fast printing allows switching all print mode from 8 kHz (1 kB/s) to 256 kHz (32 kB/s) by default.

• It also supports running in GBC mode, doubling the base speed of transfer, which should become 16kHz
• There's also a fast print in GBC mode, that would be 512 kHz

I'm also a user of NeoGB Printer, based on ESP32 it implements the Gameboy Printer Serial IO code from this project, previously it was using a version of the code from 2020 and double speed mode wasn't compatible, I upgraded the code to the serial code the most recent version and I was pleased to find out that now double speed mode works too in GBC mode.

Now I'd like request support for these faster printing modes, I'm not sure if the microcontrollers would be able to support 512kHz but there's a chance that 256kHz could work

Here's a project that supports fast printing on a raspberry pico:
https://github.com/untoxa/pico-gb-printer