# What this PR does
- Adds [`mypy` static type checking](https://mypy-lang.org/) to our CI
pipeline. Currently there is still a **ton** of errors being returned by
the tool, as we'll need to fix pre-existing errors. I think we can
slowly chip away at these errors in small PRs, doing them all in one
large PR is likely very risky.
- Also, this PR starts chipping away at one of the main type errors that
we have which is accessing the `datetime` class (from the `datetime`
library) or `timedelta` function on the `django.utils.timezone` module.
Basically we should be instead accessing these two objects from the
native `datetime` module. This makes sense because the [`__all__`
attribute](https://github.com/django/django/blob/main/django/utils/timezone.py#L14-L30)
in `django.utils.timezone` does not re-export `datetime` or `timedelta`.
- splits `engine` dependencies out into `requirements.txt` and
`requirements-dev.txt`
## Checklist
- [ ] Unit, integration, and e2e (if applicable) tests updated (N/A)
- [ ] Documentation added (or `pr:no public docs` PR label added if not
required) (N/A)
- [ ] `CHANGELOG.md` updated (or `pr:no changelog` PR label added if not
required) (N/A)
