Maybe support PyPy using cpyext?

Maybe this is helping:

https://doc.pypy.org/en/latest/release-v7.3.1.html
>Conda Forge now supports PyPy as a python interpreter.

I'm not pushing for this (it's not high-priority, would only make faster, maybe more secure), I just noticed they use UTF-8 (and CPython does Unicode, still, differently), like Julia so might be a no-copy to/from Python if it's PyPy.

Even if we do not do this, their UTF-8 implementation is intriguing with optional O(1) indexing, into variable length UTF-8 (something Julia should consider doing, possibly PyPy [code] could help?).

https://doc.pypy.org/en/latest/faq.html#what-about-numpy-numpypy-micronumpy

Depending on status of this, PyPy could be safer:
https://doc.pypy.org/en/latest/sandbox.html

I think they also use ordered Dicts, not sure (either way should work, with it we need to consider changing PyCall, need to anyway, see my other issue on that):
https://twitter.com/pypyproject/status/942070907715182592?lang=en