Add GitHub Action mypy.yml to mypy --ignore-missing-imports

[cclauss]

Describe your change:

Add testing for #4052 by running mypy --ignore-missing-imports on all directories that currently pass mypy tests.

I tried to add mypy testing to our pre-commits but #4272 was more pain than it was worth.

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?
• Add GitHub Action mypy.yml

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[dhruvmanila]

The thing with mypy is it needs the additional dependencies for it to able to carry out the checks properly. This means we should add the job to our existing CI which already installs the dependencies.

[cclauss]

--ignore-missing-imports

[dhruvmanila]

The flag --ignore-missing-imports is only for the imports whose types are missing. mypy usually complains if the type hints are missing from any imported module. This flag will make the type hint for those modules as any.

For the modules which do contain type hints, they will be used by mypy to do the validation even if this flag was passed.

[cclauss]

Closing in favor of #4276