types(power_sort): preserve input item type

[nightcityblade]

Summary

• Preserve the input item type throughout PowerSort and its internal helpers.
• Accept any iterable, matching the algorithm's existing copy-before-sort behavior.
• Add PowerSort to the shared comparable-items and mixed-type regression tests.

Part of #15234 (intentionally not closing the tracking issue).

Tests

• uv run --no-sync pytest sorts/power_sort.py tests/test_sorts.py --doctest-modules -q (459 passed)
• uvx pre-commit run --all-files --show-diff-on-failure
• uvx ty check sorts/power_sort.py tests/test_sorts.py

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".

N/A for the final item: #15234 explicitly requests Part of #15234 without a closing keyword because it tracks multiple algorithms.

[nightcityblade]

Rebuilt the approved change on current master to resolve the conflict. The 459 focused tests, full pre-commit suite, and Ty all pass.