devel/py-pytest-run-parallel: Add py-pytest-run-parallel 0.3.1

pytest-run-parallel is a simple pytest plugin to run tests concurrently.

This pytest plugin takes a set of tests that would be normally be run serially
and execute them in parallel.

The main goal of pytest-run-parallel is to discover thread-safety issues that
could exist when using C libraries, this is of vital importance after PEP703,
which provides a path for a CPython implementation without depending on the
Global Interpreter Lock (GIL), thus allowing for proper parallelism in programs
that make use of the CPython interpreter.