maths: add weighted_average function

[liyana3572]

Description

I added a weighted_average function to maths/weighted_average.py that computes the weighted arithmetic mean of a list of values given corresponding weights, with input validation.

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• 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 include at least one URL that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".

[zuhairkazmi14]

The implementation is clean and follows PEP8 style conventions perfectly. The inclusion of doctests for empty lists, mismatching lengths, and zero-sum weights is excellent. One minor optimization: instead of if not values and not weights:, since you check length mismatch immediately after, you could simplify this by checking if the values list is empty first: if not values: raise ValueError('Inputs cannot be empty'). This is cleaner and correctly catches empty lists even if one of them was passed with elements. Otherwise, great work!