sorts: make recursive mergesort generic for comparable items

[ColumbusLabs]

Describe your change

sorts/recursive_mergesort_array.py now sorts any mutually comparable items, not only integers. It accepts an iterable, copies it, and returns a new list. Doctests cover strings, mixed floats and ints, a non-list iterable, and the TypeError raised when items cannot be compared. tests/test_sorts.py runs this sort through the shared comparison-sort cases, including the non-comparable failure.

Part of #15234

• sorts: make algorithms sort any comparable items, not just ints #15234

How this was verified

python3 -m doctest -v sorts/recursive_mergesort_array.py
python3 -m pytest tests/test_sorts.py sorts/recursive_mergesort_array.py -q --tb=short
python3 -m ruff check sorts/recursive_mergesort_array.py tests/test_sorts.py

Doctest: 12 passed. Pytest: 297 passed. Ruff: all checks passed. These ran with Python 3.12.3. The repository targets Python 3.14; that interpreter was not available locally.

• 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".

[cclauss]

Nice!