fix: update tests.py to pass, add to github workflow

[tringenbach]

As I mentioned on my other PR, I noticed that tests.py was failing, looks like the code under test changed out from under it over time. This gets it all passing again. I added it to the github workflow, so that hopefully they can be more useful.

For the colour and white light tests, the values changed. I am assuming the new ones are correct, just for a different variant. I left the old ones commented out.

I reworked how the tests use mocks. I change them to use return_value instead of side_effect, and to grab the "results" (really, what the library wanted to send) from .call_args. That allowed me to eliminate a separate mock function for each test.

The also now mostly deals with Python dicts instead of decoding the binary format. That is mainly because of how _send_receive works. (I assume it used to not do that decoding, but I didn't really dig into the history).

I also added section comments, the standard-ish "arrange" / "act" / "assert" comments plus "gather results" and "expectations". I can remove those if you don't like them of course. Personally I like to at least have an "act" or "execute" comment in my unit tests, because I find that line, which is the important thing-you're-actually-testing line, often gets lost among all the setup code.