Add Cosine Similarity algorithm to machine_learning

[sanjeevi0078]

Description

This function calculates the cosine similarity between two vectors, raising errors for mismatched lengths or zero-vectors. It includes doctests for validation.

Describe your change:

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

[sanjeevi0078]

Hey everyone! Added a clean, pure-Python implementation of Cosine Similarity to the machine_learning directory. Figured it’s a super foundational metric that was missing. Let me know if anything needs tweaking!