Distinguish unit tests vs integration tests

[delucchi-cmu]

Creating tiers of test targets could reduce typical test-driven-development build cycle times.

[delucchi-cmu]

• [x] run black / isort
• [ ] add pytest.mark.slow to pytest configuration and mark tests that are > 1s as @slow
• [ ] make sure tests can be run in any order (may spawn further actions to achieve)
• [ ] modify CI to run pytest "not slow" and then pytest "slow"

[eacharles]

We probably want to integrate this in to the template for the relevent github workflows and then push it to various repos.

[eacharles]

This is large done by moving the longer stuff to the notebooks where are run in the rail smoke tests.