Add mypy config, CI, and fix type

[mkly]

• Update pyproject.toml config for jq
• Add mypy check to CI
• Fix small type issue so mypy passes

[github-actions]

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[mkly]

As mentioned in the previous PR, 100% okay we would rather not add this. Just easy stuff to do while I'm learning the code base.

[wpietri]

Sorry, I'm not getting the intent of this PR. What are you looking to improve?

[mkly]

Apologies, I should have provided more context. As you probably noticed, I added the black check to CI. When doing that on newhelm it was suggested that I also add a check with mypy. I was applying that check here and the changes relate to getting the mypy test to pass locally and in CI.

I can certainly understand if you would prefer not to add this, so if you would rather close this out, no problem at all.

[wpietri]

Let's all discuss it. Putting a tool in CI shifts it from being a supportive relationship to a controlling one. I'm grudgingly OK with that for black, but I have more concerns about mypy, especially on a project that's still pursuing product-market fit.

[mkly]

Closing as per morning discussion. Thanks.