machine_learning: add RidgeRegression with tests and demo

[Mahadev-05]

Describe your change:

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

Description

This pull request adds a Ridge Regression algorithm with L2 regularization, implemented using batch gradient descent.

The implementation:

• Is written from scratch without using external machine learning libraries
• Applies L2 regularization while excluding the bias/intercept term
• Uses clear function and variable naming with Python type hints
• Includes input validation and comprehensive doctests
• Is implemented as a pure algorithm with no file I/O, printing, or plotting

Reference:
https://en.wikipedia.org/wiki/Ridge_regression

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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.
• This pull request resolves one or more open issues (not applicable).