sorts: type intro sort for comparable items

[Felix-ming]

Describe your change

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

Type IntroSort and its helpers for mutually comparable items. This adds coverage for numeric and string inputs and verifies that mixed incomparable values raise TypeError.

Part of #15234

Checklist

• I have read CONTRIBUTING.md.
• This pull request is all my own work.
• I understand automated tests must pass before merge.
• This PR changes one algorithm implementation.
• All new Python files are in an existing directory.
• All names follow Python naming conventions.
• All function parameters and return values are annotated.
• All doctests pass under the supported Python version.

[cclauss]

@priya-sundaram-dev, please review.

[cclauss]

Please add to tests/test_sorts.py the line from sorts.intro_sort import sort as intro_sort and then add intro_sort to the SORTS tuple and @pytest.mark.parametrize list.

[priya-sundaram-dev]

LGTM — the PEP 695 generic conversion is correct. I ran the doctests on Python 3.12 (41/41 pass) and spot-checked further:

• The median_of_3 rewrite to use only < (to match the Comparable protocol's single __lt__) is behavior-preserving: a > b ⇔ b < a, so both != branches are logically identical to the originals. Verified equal on 3000 random 3-element inputs.
• 2500 random int/str arrays sort identically to sorted().
• The new sort([1, 'a']) doctest raises TypeError as expected.

One note for @Felix-ming: per cclauss's comment, wiring intro_sort into the existing tests/test_sorts.py SORTS tuple (rather than the standalone tests/test_intro_sort.py) keeps the suite consistent. Otherwise this is clean.