Use testthat 3

[olivroy]

I also silenced a couple of tests / output along the way.

[olivroy]

Thanks for triggering CI. As you see, there is still a lot of noise in the logs. I will try silencing most of it. It is mostly due to the fact that packages loaded in broom's tests are quite noisy on load. (when clicking on show testthat output)

[simonpcouch]

Noise in the logs is okay! What's more important is my ability to understand the change set comprehensively. As-is, there are still many changes that seem unrelated to the switch to testthat 3e—I'd welcome those other changes in separate PRs where their scope is more clearly defined, but will ask you to further pare back the changes here to only those needed to related to switching to 3e.