Added apr_interest function to financial

[smturro2]

Describe your change:

In almost every scenario financial institutions will give the APR for a loan or credit card. This function allows you to calculate the interest without having to calculate the effective interest rate from the APR.

• 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}.

[smturro2]

Hi, is there additional changes that need to be made to proceed with the pull request? Thanks!

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[tianyizheng02]

@cclauss I think this is good to merge as long as it passes the current workflows

[tianyizheng02]

mypy.....................................................................Failed
- hook id: mypy
- exit code: 1

financial/interest.py:113: error: Argument 3 to "compound_interest" has incompatible type "float"; expected "int"  [arg-type]
Found 1 error in 1 file (checked 1192 source files)

pre-commit is failing because of a mypy error in a different function in the same file

[tianyizheng02]

The compound_interest function call in apr_interest is causing mypy to fail because compound_interest takes an int for the number of compounding periods:

def compound_interest(
    principal: float,
    nominal_annual_interest_rate_percentage: float,
    number_of_compounding_periods: int,
) -> float:

We should change the type hint for number_of_compounding_periods from int to float.