Further improvement of parameter operator test implementation

[heplesser]

This PR makes the parameter operator tests even more readable and efficient. It is a follow-up to #2628.

Concerning efficiency, tests using Py 3.11 indicate that using hasattr() instead of try-except improves performance by almost half.

One could argue that the test code here would become even simpler of the nest Parameter objects supported direct casting to int or float. But these parameters are only to be evaluated inside the C++ kernel, so adding __int__() or __float()__ methods at the Python level would only simplify test-writing, with no bearing on actual use. But writing code for the sake of testing only seems not sensible.

[heplesser]

I dug deeper into the xfail documentation and found that one can mark individual cases explicitly as xfail, while cases that should pass can be provided as usual. I hope you like the new implementation.

[nicolossus]

This looks very nice! I'm guessing the newly added .bak file is unintentional and should therefore be removed before merge.

[heplesser]

This looks very nice! I'm guessing the newly added .bak file is unintentional and should therefore be removed before merge.

Thanks for noticing, I have removed the file again.

[jougs]

Just a small typo. Otherwise nice work!