Add Andrew's Monotone Chain convex hull algorithm

[Clear20-22]

Describe your change:

Add Andrew's Monotone Chain algorithm for computing the 2D convex hull of a set of points in O(n log n) time.

• 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".

[Copilot]

🟢 Approval recommended

The new module is self-contained, correctly implements the monotone chain approach, and includes adequate doctest coverage plus references consistent with existing geometry modules.

Pull request overview

Adds a new computational-geometry algorithm module implementing Andrew’s Monotone Chain method for computing the 2D convex hull, consistent with the repository’s educational, doctest-driven style.

Changes:

• Introduces geometry/monotone_chain.py implementing monotone_chain() with a Point representation and a cross-product orientation helper.
• Adds thorough doctest examples covering empty input, duplicates, interior points, and collinear inputs.
• Documents time/space complexity and provides a Wikipedia + paper reference.

File summaries

File	Description
geometry/monotone_chain.py	New convex hull implementation (Andrew’s Monotone Chain) with supporting Point type, orientation helper, and doctests.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Lite

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