Describe your change:

• Documentation change?

Added a clear Complexity Analysis section to the insertion_sort function docstring inside sorts/insertion_sort.py.

It documents:

• Time Complexity: Best Case $O(n)$, Average Case $O(n^2)$, and Worst Case $O(n^2)$.
• Space Complexity: $O(1)$ auxiliary space.

Fixes #14866

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 have 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 Improve docstrings in insertion_sort.py to include complexity analysis #14866".

Fixes #14866