Merging branch 'm.i875'  into 'main'.

See merge request !2728

Merging branch 'a.rmCpp20'  into 'main'.

See merge request !2727

Avoid using C++20 features to keep the libraries maintainable on older systems.

Merging branch 'm.i972'  into 'main'.

See merge request !2726

Merging branch 'a.newNumpyInterface_rmNumpy'  into 'main'.

The Numpy C-API is removed from the build mechanism.
Numpy Python package is needed only for tests.

* Removed the references to the Numpy C-API from the `PyCore` module.
* Removed SWIG include file `Wrap/Swig/numpy.i` and updated `Wrap/Swig/commons.i`.
* Updated the tests.
* Updated SWIG-produced C++ wrappers.


See merge request !2724