CI improvements for non-x86 architectures

[hugsy]

Currently GEF is only being tested as such:

1. bunch of pytest that can run anywhere, and are triggered by every push/pr by Github Actions - but only covers x86/x64 architectures
2. before every release, I use my Raspis and Qemu VMs to manually run the same tests

This thread is an open forum to discuss possible solutions to improve the 2nd point, bringing it closer to point 1 (i.e. fully automated CI for all arches). I've tried Qemu on GithubActions default runners and it's way too slow - time of 1 run for qemu-mips would take ~30min to finish. So it's not practical.

A possible Github Actions feature we could use is deploying custom runners, but that would require running untrusted code on a device/vm, with all that comes with it. I have tested it on one of my rpi4 and this works well. If we find a way to hosting it securely we could also consider extending this to other dev boards such as:
* RISCV dev board
* MIPS dev board
* support Windows on ARM with a custom ARM64 dev board or a Project Volterra
* and even with a dedicated MacOS Mini - since I'm not much an OSX person myself

We're open to new suggestions and ideas so don't be shy to contribute here with your 50c.