added type hints and doctests to arithmetic_analysis/intersection.py

[spamegg1]

continuing #2128

Describe your change:

• Fix a bug or typo in an existing algorithm?

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 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.

[spamegg1]

Let's hope it goes better this time!

[itsvinayak]

@cclauss please have a look

[cclauss]

The variable names (x0, x1, x_n, x_n1, x_n2), etc. make my head spin but these changes look good to me.

[spamegg1]

The variable names (x0, x1, x_n, x_n1, x_n2), etc. make my head spin but these changes look good to me.

I didn't want to change the existing algorithm too much. Maybe some cosmetic changes in the future.

Thanks for the reviews and approvals everyone!