Add a tox environment to run mypy for static type checking - #15815

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Does this supersede #15794 ?

Thank you for the question! It's more like this PR depends on #15794 rather than superseding it. These PRs are two of the three steps that we took for adding mypy to PlasmaPy's CI suite:

1. Configure mypy.ini so that running mypy ignores all current errors, which could be done with either of these PRs:

• Add mypy configuration file that ignores existing errors on a per-file and per-error basis #15794
• mypy incremental adoption settings #12971

2. Add a tox environment for running mypy (this PR)
3. Add a GitHub Action that uses the tox environment (akin to Add mypy to continuous integration suite PlasmaPy/PlasmaPy#2432)

I wanted to separate the PRs in case there's a decision to take a different approach than #15794.

A follow-up to this exploratory PR: I mentioned in this post that it's worth considering alternatives to mypy such as pyright.

@namurphy, I'm in favor of this! mypy and pyright are sufficiently similar we can start with one and switch to the other, should the need arise. Since mypy is considered the baseline, I think it's good to start with it. This would be a good PR to get in for v7, so maintainers test their type hints!

Hi humans 👋 - this pull request hasn't had any new commits for approximately 4 months. I plan to close this in 30 days if the pull request doesn't have any new commits by then.

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I'm going to close this pull request as per my previous message. If you think what is being added/fixed here is still important, please remember to open an issue to keep track of it. Thanks!

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