refactor(sorts): remove redundant TypeVar in pancake_sort

[iosayin]

Describe your change

• 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?

Removes the redundant TypeVar import and T = TypeVar("T", bound=Comparable) definition in sorts/pancake_sort.py, relying directly on Python 3.12+ PEP 695 generic parameter syntax [T: Comparable].

Reference: #15234

Checklist

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
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• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
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