docs: clean up docstring in fib_recursive function

[sharvandeep]

This PR improves the docstring for the fib_recursive function in maths/fibonacci.py.

• Clarified summary description
• Added properly formatted Args and Returns sections
• Fixed example test cases with correct function name
• Ensured consistent formatting across docstrings

This is part of issue #13948 — cleaning and standardizing docstrings.

Checklist:

• [x] Follows docstring format used in repo
• [x] Tested formatting locally
• [x] Only documentation updated

Thanks!

[sharvandeep]

All checks have passed. This PR addresses issue #13948 by improving the docstring for fib_recursive. Kindly requesting a review when convenient. Thanks!