docs: Add type hints and improve documentation for pancake_sort

[2400031832]

Describe your change:

This PR improves the documentation for the pancake_sort.py file to address issue #13948 about documentation inconsistencies.

Changes made:

• Added comprehensive module-level docstring explaining the Pancake Sort algorithm
• Added type hints to the function signature using list[Any]
• Added detailed docstring with Args, Returns, Time Complexity, and Space Complexity sections
• Added inline comments explaining each step of the algorithm
• Added additional doctest examples for better testing coverage
• Added time complexity (O(n^2)) and space complexity (O(1)) documentation

• [ ] Add an algorithm?
• [ ] Fix a bug or typo in an existing algorithm?
• [ ] Add or change doctests?
• [x] Documentation change?

Checklist:

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized.
• [x] I know that pull requests will not be merged if they fail the automated tests.
• [x] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.