Two years of test item framework updates

It has been about two years since my last update on the test item framework, and a lot has happened in the meantime, so here is a roundup. A quick recap for anyone who has not come across it: the test item framework lets you write your tests as independent @testitem blocks instead of one large nested @testset tree. Each test item runs in its own module, declares its own dependencies and tags, and — this is the whole point — can be run on its own, in parallel with others, and from wherever you h...