Enhance docstring with complexity analysis

[2400031832]

Added time and space complexity analysis to the selection_sort function docstring.

Related to #13948 - Documentation inconsistencies

Describe your change:

• [x] Documentation change?

Changes:

• Added Time Complexity: O(n^2) to selection_sort docstring
• Added Space Complexity: O(1) to selection_sort docstring

This improves documentation consistency by adding complexity analysis that helps beginners understand the algorithm's performance characteristics.

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.