End-to-end tests that make sure the activity/lightcurve classes work?

[astronomerritt]

Seeing as I've just made this issue and this issue, I think we need two more end-to-end tests that make sure Sorcha successfully produces output when activity or lightcurve subclasses are used...

However, this does require that sorcha-addons is installed into the environment tests are run on, including the GitHub actions.

[astronomerritt]

Closing and opening on the sorcha-addons repo.