Run tests against ecosystem packages

src/validation.rs has code to run src/verify_distribution.py to check behavior against the stdlib, but we should also have some tests against third-party packages, including at least
* old versions of python-mscl and ucxx (#619), may as well test new versions too
* matplotlib and PIL.TkImage, both likely requiring a display server (details and reproducer in #129)
* various packages with musllinux wheels (details and reproducers in #724)
* PyInstaller, probably as an end-to-end test (see e.g. #742)

Not sure if there's a benefit in running test with both pip and uv. pip is already shipped inside the distribution, so probably we should at least test with it.