Build with non Python files
# What does this PR do?

It appears the non python files (such as CUDA kernesl) have disappeared from the built package once again. Fir some reason there were found before with just `*.extension`, but now need `**/*.extension` (although once found again I can remove the **).

This is all super brittle, so this PR also adds:
- a check that the build package contains the non-Python files before we upload it on testpypi
- a check that the library installed does contain the non-Python files before we upload it on pypi

Will make a patch after this is merged.
_The documentation is not available anymore as the PR was closed or merged._