Add docstring and type hints to two_sum

[gokul000410]

Description

This pull request adds a detailed docstring and type hints to the two_sum implementation in the arrays section.

The changes improve code readability and maintainability while keeping the existing algorithm logic unchanged.

Changes Made

• Added a clear docstring explaining the approach
• Added type hints for better clarity

Checklist

• [x] Code follows repository style guidelines
• [x] No functional changes were made