for testing purposes

[parthea]

Prototyping for #521

[parthea]

In PyPy3.10, we see the following warnings

upb

UserWarning: Selected implementation upb is not available. Falling back to the python implementation.

nox > pytest --quiet --cov=proto --cov-config=.coveragerc --cov-report=term --cov-report=html tests
ImportError while loading conftest '/home/runner/work/proto-plus-python/proto-plus-python/tests/conftest.py'.
tests/conftest.py:18: in <module>
    from google.protobuf import descriptor_pool
.nox/unit-pypy3-10-implementation-upb/lib/pypy3.10/site-packages/google/protobuf/descriptor_pool.py:41: in <module>
    from google.protobuf import descriptor
.nox/unit-pypy3-10-implementation-upb/lib/pypy3.10/site-packages/google/protobuf/descriptor.py:20: in <module>
    from google.protobuf.internal import api_implementation
.nox/unit-pypy3-10-implementation-upb/lib/pypy3.10/site-packages/google/protobuf/internal/api_implementation.py:100: in <module>
    warnings.warn('Selected implementation upb is not available. '
E   UserWarning: Selected implementation upb is not available. Falling back to the python implementation.

cpp

UserWarning: PyPy does not work yet with cpp protocol buffers. Falling back to the python implementation.

nox > pytest --quiet --cov=proto --cov-config=.coveragerc --cov-report=term --cov-report=html tests
ImportError while loading conftest '/home/runner/work/proto-plus-python/proto-plus-python/tests/conftest.py'.
tests/conftest.py:[18](https://github.com/googleapis/proto-plus-python/actions/runs/12907499279/job/35991059988?pr=523#step:5:19): in <module>
    from google.protobuf import descriptor_pool
.nox/unit-pypy3-10-implementation-cpp/lib/pypy3.10/site-packages/google/protobuf/descriptor_pool.py:63: in <module>
    from google.protobuf import descriptor
.nox/unit-pypy3-10-implementation-cpp/lib/pypy3.10/site-packages/google/protobuf/descriptor.py:40: in <module>
    from google.protobuf.internal import api_implementation
.nox/unit-pypy3-10-implementation-cpp/lib/pypy3.10/site-packages/google/protobuf/internal/api_implementation.py:65: in <module>
    warnings.warn('PyPy does not work yet with cpp protocol buffers. '
E   UserWarning: PyPy does not work yet with cpp protocol buffers. Falling back to the python implementation.
nox > Command pytest --quiet --cov=proto --cov-config=.coveragerc --cov-report=term --cov-report=html tests failed with exit code 4
nox > Session unit-pypy3.10(implementation='cpp') failed.

[parthea]

The failure below should be fixed with #507

https://github.com/googleapis/proto-plus-python/actions/runs/12907548308/job/35991217125?pr=523

            else:  # Python 3.11.0b3
>               del attrs._member_names[pb_options]
E               TypeError: 'set' object does not support item deletion

proto/enums.py:65: TypeError

Closing this PR. I'll incorporate the new PyPy presubmit into the existing PR #507