Don't call self from subprocess for tests #285
Description
Motivation
Now that we have codecov, I can see the slow tests:
https://app.codecov.io/gh/nathanjmcdougall/usethis-python/tests/main?parameter=SLOWEST_TESTS
We should use #190 for these cases. The overhead of importing typer etc. slows things down significantly.
Summary of desired enhancement
Speed up tests by never calling usethis as a subprocess.