Add adjacency representation generator for closed Hamiltonian tours

[Naman-Vasudev]

This pull request adds a new algorithm that converts a path (permutation form) of a closed Hamiltonian tour into an adjacency representation vector.
Each position in the resulting vector corresponds to a city (in fixed alphabetical order), and the value at that position denotes the next city in the tour.

[priya-sundaram-dev]

Thanks @Naman-Vasudev — clear docstring, type hints and doctests, and the closed-tour wrap-around logic reads well.

One robustness suggestion: next_city_map.get(city, "-") silently yields "-" when a node in nodes never appears in path. Since a valid tour should visit every node, I'd validate set(path) == set(nodes) up front and raise a ValueError on mismatch, so malformed input fails loudly instead of producing a "-" placeholder.

This pairs with your #13647 (ordinal representation) — both are TSP tour encodings used in GA crossover. It might read more cohesively if the two docstrings cross-reference each other (or live together), so a reader sees them as a family of representations.

[cclauss]

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