[itsnevu]

Describe your change

Makes double_sort generic over any Comparable items instead of list[Any], following the already-merged insertion_sort.py pattern (a Comparable Protocol plus a [T: Comparable] type parameter). Comparisons already go through < only, so items only need __lt__.

Part of #15234 (using "Part of", not a closing keyword, so the umbrella issue stays open).

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

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 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. New doctests cover a str list, a float/int mix, and a pytest.raises(TypeError) for non-comparable input.

[cclauss]

ON HOLD: Our focus is on merging or closing old pull requests before October 1st.

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