testing/py3-setuptools-rust: new aport

Adds in a python dependency that is needed to package !26713 (closed). Has checks that are run officially (in its CI pipelines) using tox which uses network access. py3-setuptools-rust also downloads a bunch of rust crates during the test phase. Other aports seem to do this as well, but if there is a strong recommendation against this, I can either try and work on patches or disable tests. The package will have to be moved to community to unblock that aspect of !26713 (closed).