Added type hints and doctest for maths/prime_check.

[frangiz]

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

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}.

[frangiz]

Should I remove all the unittests and move some of them to the doctest instead?

[cclauss]

There are two main kinds of tests built into Python:

• https://docs.python.org/3/library/unittest.html
• https://docs.python.org/3/library/doctest.html

Given that this file already has strong unittest coverage, it does not also need doctests. The typehint is useful however.

[frangiz]

@cclauss , I have updated the PR according to your comment. Let's say I fix a bunch of type hints, still want one file per PR (as mentioned in contributing.md) or is a few together OK for things like this?

[cclauss]

Nice work!! Thanks.

[cclauss]

One file per commit please (my brain power is limited). ;-)