Use wrappers to complete SciPy and NumPy interface namespaces

[ndgrigorian]

This PR proposes using wrappers for fftfreq, fftshift, ifftshift, and rfftfreq instead of importing them from scipy.fft or numpy.fft directly

These thin wrappers can avoid infinite recursion of dependencies, i.e., when importing Intel NumPy with Intel SciPy in the environment

[antonwolfy]

The fix LGTM! But need to add the PR to the changelog also.

[ndgrigorian]

The fix LGTM! But need to add the PR to the changelog also.

done

[ekomarova]

Will a change like this always require scipy as a mkl_fft dependency, or can it still be optional?

[ndgrigorian]

Will a change like this always require scipy as a mkl_fft dependency, or can it still be optional?

It can still be optional—since the scipy interface is only exposed in interfaces/__init__.py if SciPy can be imported, this doesn't change anything (scipy_fft.py already needed to import it before)

alternatively, the import could be made lazy, so we could do from scipy.fft import fftshift in the def of fftshift.