Thanks, I will add an __all__

_zipimport_get_resource_reader gets called from C and it's the way we trampoline from the inscrutable zipimport.c into something we can more reasonably implement the ResourceReader API.  There's a comment above _ZipImportResourceReader but do you think that's easy to miss or misunderstand?

The use of builtins_open is historical; the importlib.resources name used to be `open`.  I think we can get rid of this cruft, as it's just an implementation detail.

I'll work on a PR