Suspicion of endianess issue

[tardyp]

Hello,

With maturin default settings, the CI automatically checks on big endian platforms such as s390x and ppc64.

On those platforms, my test fail with error like:
https://github.com/tardyp/protoxy/actions/runs/9997525350/job/27634293608

As those are the two only bigendian platform I think this must be some endianess issue.
This is most probably a problem in upb which is the backend of python's protobuf (written in C)
but I figure this might be interrsting for you to know.