style: correcting all outstanding mypy errors

[ns-rse]

Closes #32

Fixing almost all outstanding mypy typing errors.

There are a few where I have used the # type: ignore[<rule>] as I couldn't work out how to resolve things but this
should mean that mypy passes both locally and in pre-commit.ci and so going forward we can stay on top of the
type-hints and ensure things always pass.

Explicitly exclude tests/ from type checking.

---

Before submitting a Pull Request please check the following.

• Existing tests pass.
• Documentation has been updated and builds.
• Pre-commit checks pass.
• New functions/methods have typehints and docstrings.
• New functions/methods have tests which check the intended behaviour is correct.

[ns-rse]

pre-commit.ci is failing as its running on tests/ this pull-request includes removal of tests from the mypy
configuration of pyproject.toml and so subsequent to this being merged that directory should be ignored and
pre-commit.ci should pass.

[fisher568]

mypy passes on my machine if I run it as part of pre-commit (e.g. by making a perfunctory change and attempting to commit it). I think this is good to merge, but why is the tests folder explicitly being ignored now, I get quite a few failures when I run mypy on all files?

[ns-rse]

why is the tests folder explicitly being ignored now, I get quite a few failures when I run mypy on all files?

I was keen to get the src/ directory passing and keep pull requests small and incremental. I too have mypy failing on tests/ but I'm mindful of time and want to push on with the dataclasses and felt my time would be better spent focusing on that.

I've noted it as a task in #115.

Thanks for the ✅