run_under_venv

Problem

Even if protoprimer aims at starting without venv to initialize a venv, it should work without issues when started under already activated venv (regardless whether it is related or unrelated venv) and initialize the required venv.

Solution

When venv and path to proto_code was not specified, switch out of this venv (escape) to the python (sys.base_prefix) used by this venv.

Actually, it should isolate itself not only from venv but from any deployed non-standard packages. See isolated_python.