fix(sorts): accept lt-only items in recursive insertion sort

[tuttucodes]

Describe your change

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Existing doctests remain unchanged.
• Documentation change?

insert_next used <=, so a collection whose elements implement only < raised TypeError even though those elements are orderable. Compare the next element with < instead and bind the generic type parameter to Comparable. Add a shared regression case with a custom <-only element. Existing sort tests cover strings, floats, and the mixed-type TypeError case.

Part of #15234. This is one algorithm from the umbrella issue, so the issue should remain open.

Verification

• python3.14 -m doctest sorts/recursive_insertion_sort.py
• uvx --python 3.14 pytest tests/test_sorts.py -q — 384 passed
• uvx ruff check sorts/recursive_insertion_sort.py tests/test_sorts.py
• uvx ruff format --check sorts/recursive_insertion_sort.py tests/test_sorts.py
• uvx pre-commit run --all-files

Checklist

• I have read CONTRIBUTING.md.
• This pull request is original work and does not copy another implementation.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file and its shared regression test.
• All modified function parameters and return values have type hints.
• The existing algorithm functions have passing doctests.
• All new Python files are placed inside an existing directory. -- No new files.
• All new algorithms include an explanatory URL. -- No new algorithm.
• This PR closes an issue. -- sorts: make algorithms sort any comparable items, not just ints #15234 tracks several remaining algorithms.