Replace pfUnit?

### Are there any linked Issues or Pull Requests?

_No response_

### Brief description

Maintaining pfUnit for different compilers is an overhead. Furthermore, we don't get any particular benefit of pfUnit unit test features.

It may be better to write our own test runner that takes into greater account the need for command line testing (such as re-testing only modified tests).

### Further details of the issue.

_No response_

No files, tests, or entry points are named. Start by locating the repository's pfUnit usage and how tests are currently invoked from the command line. Define the replacement runner's scope, including compiler support and rerunning only modified tests, before implementation; completion would require agreement on that design and successful migration of the existing tests.

Written by the indexing model from the issue text.