[trleo]

Describe your change

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

Fixes #15655. continued_fraction used floor(numerator / denominator), converting huge integers to float. That rounded 2**53+3 up, giving [9007199254740996, -1] instead of [9007199254740995], and raised OverflowError for Fraction(10**400, 3). This change uses exact integer floor division numerator // denominator, removes the now-unused floor import, and adds a regression doctest for Fraction(2**53 + 3).

Tested on Linux: python -m doctest maths/continued_fraction.py passes 9 tests, ruff check and ruff format pass. Ruff/pytest via uvx were not available in this environment, so CI should confirm those.

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.
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• If this pull request resolves one or more open issues, then the description above includes the issue number(s) with a closing keyword: "Fixes continued_fraction uses float division, producing invalid terms for large integers and raising OverflowError #15655".