Add notebook smoke tests, other QOL changes

[matthewcarbone]

Just playing around/exploring the code a bit. While I was I figured I'd make a few QOL changes to the testing system:

• Trying something new by adding a smoke test to the notebook. Figured it could be useful considering the notebooks are hosted on Colab and should always work. It's a fun hack that you can use: ipython -c "%run simpleGP.ipynb", for example.
• Added osx-latest to the runs-on in the testing jobs. Since the project is open source your CI hours are free so it doesn't matter that it's a more expensive OS to test on.
• Added python version 3.11 to the list of tested versions.

(there will no doubt be bugs which I will fix 👍)

[matthewcarbone]

Forgot to pull from upstream, I'm gonna cherry pick and reopen another PR.