fix(sorts): make smoothsort generic over Comparable items

[wanjinhao1]

Describe your change

• 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".

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Part of #15234 (does not close the tracking issue).

What

• Adds the shared Comparable protocol (__lt__ only) and a TypeVar bound so smoothsort (and its helpers _sift / _trinkle) accept any list of mutually comparable items (list[T]) instead of list[int].
• Rewrites all comparisons in _sift and _trinkle to use only < (the protocol guarantees nothing else): >= becomes not (a < b) and a > b becomes b < a, preserving stability semantics for total orders.
• Adds doctests for strings, mixed int/float input, and the mixed-type TypeError failure mode (smoothsort([1, "a"])).
• Registers smoothsort in the shared SORTS battery in tests/test_sorts.py, which also covers the non-comparable rejection case.

Why

smoothsort.py is one of the remaining unchecked comparison sorts in the #15234 checklist, with no open PR and no assignee.

Validation

• python3 -m doctest sorts/smoothsort.py — all doctests pass (including the new string/float/TypeError cases)
• python3 sorts/smoothsort.py — all doctests plus the built-in 5,000 random trials pass
• python3 -m pytest tests/test_sorts.py -q — 394 passed (smoothsort now runs across the full shared CASES battery, including Person/Dog dataclasses, and the [1, "a"] rejection test)

Note: one algorithm per PR per the tracker guidance. This PR was completed with AI assistance under the supervision of the account owner (@wanjinhao1) — happy to address any review feedback.