Add Trapping Rain Water solution in arrays

[leo-soumyajit]

Add Trapping Rain Water (LeetCode #42) implementation

This pull request introduces an efficient solution for the Trapping Rain Water problem under data_structures/arrays/trapping_rain_water.py.

Summary of changes:

Implements two-pointer algorithm for optimal trapped water calculation.
Adds input validation and edge case handling.
Includes example usage and basic test cases in main.
Provides comprehensive docstrings and problem context for educational value.

Problem details:
LeetCode: https://leetcode.com/problems/trapping-rain-water
Time complexity: O(n)
Space complexity: O(1)

Motivation:
This is a highly recommended array-based problem for interviews and algorithm practice. The complete solution, documentation, and test cases enhance clarity and learning for beginners and experienced contributors.

Checklist:
Code follows repository guidelines
Docstrings and documentation provided
Edge cases covered
Code tested locally

[algorithms-keeper]

Closing this pull request as invalid

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