Add type hints to pancake_sort function

[villenaderic]

Describe your change:

Added type hints to the pancake_sort function's parameter and return value, as requested in the linked issue.

Fixes #14737

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 add type hints to pancake_sort function #14737".

[cclauss]

Would arr="Python" fail?!? arr=[1.5, 1.3, 1.0]

[villenaderic]

Good catch floats should be supported since the docstring says "comparable items," not just ints. I have updated it to use a generic type parameter (def pancake_sort[T: (int, float)](arr: list[T]) -> list[T]) so it correctly supports both, and mypy/ruff both pass now.

[cclauss]

Perhaps https://docs.python.org/3/library/collections.abc.html#collections.abc.Hashable is the right type.