Describe your change:

This pull request adds a new algorithm that converts a closed Hamiltonian
tour (path) into its ordinal representation based on a fixed reference
order of cities. Each position in the resulting list represents the
1-indexed position of the corresponding city in the reference list,
which shrinks as each city is removed — ensuring a unique and reversible
representation.

Key Features:

• Implements ordinal_representation_closed() with descriptive variable names
• Handles closed tours (last city conceptually connects back to the first)
• Fully PEP-8 compliant (≤ 79 chars per line)
• Includes doctests verified via python -m doctest -v
• Uses modern Python type hints (list[str], int)
• Includes a reference URL for background context

• 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 function 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".