Support SPI mode (and other SPI fixes)

[kstar]

This PR addresses three issues:

1. Fix 1: I was unable to install the package under uv (astral.sh/uv), because it does not understand packages=['source/machine'] and instead wants packages=['machine'], package_dir={'machine': 'source/machine'}
2. Fix 2: I was unable to use SPI read because it looks like the helper method readfrom_into was renamed to _read_from_into, but the read method was not updated accordingly
3. SPI mode support was pending implementation, the PR implements it by adapting the firmware as well as the Python interface appropriately. Tested with mode 0x03.

Acknowledging lots of help from ChatGPT!

[PizzaProgram]

Thanks for contributing!
Sadly the owner of this repo (and other 9 repos) vanished after 2021 from here.
https://github.com/execuc?tab=overview&from=2021-12-01&to=2021-12-31

Something must have happened...

[execuc]

Hello, I’m really sorry. I haven’t worked on personal projects since 2021.
I’m getting back into it gradually. I’ll take care of the FreeCAD plugin related repo first (LCinterlocking), and then this one (issues, PRs).
Thank you for your interest in this project :)