Add a Macro Benchmark that Exercises Threading (Multi-Core Concurrency)

From @methane (https://mail.python.org/archives/list/python-dev@python.org/message/KVH7QLJ4VJBQQ45LZTWDXO2SEC6ANX7T/):

CPU cache invalidation exists regardless. With the current GIL the
effect it is reduced significantly.

It's an interesting point. We can not see the benefit from pypeformance, because it doesn't use much data and it runs one process
at a time. So the pyperformance can not make enough stress to the last level cache which is shared by many cores.

We need multiprocess performance benchmark apart from pyperformance, to stress the last level cache from multiple cores. It helps not only this PEP, but also optimizing containers like dict and set.

Inizia esaminando la suite di benchmark pyperformance esistente e il modo in cui sono organizzati i relativi benchmark a processo singolo. Definisci come un benchmark di multiprocessing dovrebbe esercitare pressione sulla cache di ultimo livello condivisa tra i core e considera il benchmark completo quando fornisce dati sulle prestazioni multi-core riproducibili e utili per valutare le ottimizzazioni di dict e set.