Migrate to Jupyterbook v2

[Songtech-0912]

Jupyterbook v2, as of January 2025, is in alpha testing. However, we should eventually upgrate to v2 as it fixes a bunch of bugs and provides a lot of more powerful features. See an example testing repo I created here.

This does, however, mean a lot of things need to be re-implemented:

• The book HTML (web) theme is not very suitable for the Project. We need to make a new custom web theme - in fact, I think the current theme is very good and making a port of the current theme (maybe with a few tweaks) to MyST would be absolutely ideal
• The book LaTeX/PDF theme is not very suitable either, it doesn't even provide syntax highlighting, and Computer Modern, while a great font for other purposes, is not a good font for print books. Adobe Source Serif would be much more suitable
• GitHub actions will have to be changed to accomodate Jupyterbook V2
• I also worry about the nature of MyST sites - they use React and this will mean it will make the docs a lot heavier and load a lot slower because it's a lot of javascript to be run client-side, as opposed to Sphinx which (I believe) is just static site + a bit of vanilla JS. Maybe some form of static site generating build step?

So we probably should develop this on a separate branch and merge things in later.