Usability improvements to unit testing

[david-pfx]

I'm working on merging the last year or so of PS changes into PuzzleScriptPlus, and there are plenty! Many of the changes depend on the test suite to confirm compatibility and to track down bugs, and it's giving me problems. It's a godsend, but it could be even better.

I would like to propose improvements to the test suite:

1. to improve the ability to run tests in groups, or by name
2. to improve the handling of errors, especially those that trigger exceptions or the ominous 'compilation aborted'.

I'm looking for feedback/suggestions/guidance. I'm happy to contribute to the work, but I'd like to know how to go about it so changes can be accepted.

[increpare]

• Improve ability to run tests in group isn't something that interests me. The tests don't take that long to run, and I like the very low overhead right now of just throwing in new tests without having to think much about what exactly they are testing 😅 . (Though I can, for instance, imagine it being useful to people developing implementations only supporting a subset of features, or incrementally adding support as they develop it, that's beyond the scope of vanilla puzzlescript).
• Giving better error output would definitely be a plus.

[increpare]

I won't do 1, and #2 is #1057 I guess