Enhance docstring for selection_sort function

[2400031832]

Describe your change:

Enhanced the docstring for the selection_sort function to address documentation inconsistencies (Issue #13948).

Changes made:

• Added a more detailed description of how selection sort works
• Added Time Complexity: O(n^2) with explanation
• Added Space Complexity: O(1) with explanation
• Kept existing examples and 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.