Create venv for whole project, rather than individual targets

[mattem]

Currently venv creation is tied to the terminal py_binary or py_test.

Under bazel this is fine and what we want, but for IDEs the user likely wants to create a venv for all the targets in their project, ie, all the test and binary targets in a given scope, or at the very least all the test targets so the IDE can run them.

This will lead to potential differences between testing under bazel and testing via the IDE as tests may have access to dependencies in the IDE that they wouldn't have under bazel.