Add reverse_string algorithm with type checking and examples

[muannn]

Describe your change:

Added the string reversal algorithm reverse_string.py:

• Implements reverse_string(s: str) -> str using slicing for reversal.
• Adds type checking (raises TypeError for non-string inputs).
• Includes module and function docstrings along with examples.
  This change, consisting of approximately 35 lines of code, expands the collection of string processing algorithms.

[mindaugl]

This is one is deep