BUG: array_api_extra.testing relies on assert statements that get stripped out with PYTHONOPTIMIZE>=1 #1068

I noticed this here, scipy/scipy#26512 (comment), when investigating mysterious CI failures in scipy/scipy#26512.

There is a SciPy CI job which sets PYTHONOPTIMIZE=2. Setting PYTHONOPTIMIZE>=1 causes assert statements to be stripped out, causing some of the checks from array_api_extra.testing to not actually be run. To fix this, I think it would suffice to replace the asserts with a helper function which does essentially the same thing. Patch incoming.