I'll address your issues in a later commit and report back.
@Fred
Indeed, I did not test the reproducibility of the build, and wrongfully assumed that switching to pybuild whilst keeping the former d/rules targets would be enough.
@Andreas
You need numpy, because setup.py makes an unconditional import of it regardless of the
target. This is a problem shared by a number of other scientific packages and it will take
time before our upstream adjust to proper practices (like do I need numpy when I invoke
python setup.py clean). These are nicely summarized at the end of the following blog post [1]. Best I can do is file a bug upstream and suggest pointers.