Detect dual test case run

[std-max]

Fix #795

Prevent from calling twice the same test case.
Reset the number of run tests when test_runner_setup is called.
Add tests.

[LarsAsplund]

The error detection looks good but I don't think we should make a the ability to re-run a test case (by calling test_runner_setup a second time) a new feature. It could be something that works just because of the way our procedures and functions are designed but the proposed error message is advertising it as a feature.

I'm afraid that unorthodox use of VUnit might lead into unforeseen complexities (just as calling a test case twice did) so I rather keep the core of VUnit structure very clean. Did you have a specific use case for this in mind?

[std-max]

@LarsAsplund In fact I added a test that calls test_runner_setup just because it was done in a previous test like the one at line 318 (banner("Should loop over enabled_test_case once and in order unless re-initialized.");
I can remove that of course as I agree with you this might be unusual !

[LarsAsplund]

@std-max Ok, I understand. I can't really recall if that test was added with a feature in mind or just to make sure that test_runner_setup is well-designed. After all, it is reasonable to expect that a setup works regardless of what happened before it. Still, I wouldn't like to make it a supported feature so if you could remove that part it would be great.

[std-max]

Done @LarsAsplund :)

[std-max]

No joke, I literally fell asleep while waiting for the checks to pass
You can now merge @LarsAsplund haha