Add N-Queens and Word Search solutions

[ravithakur2k]

Added NQueens.py implementing the N-Queens problem using backtracking, and WordSearch.py solving the Word Search problem with DFS. Both solutions include time and space complexity comments and have been tested on LeetCode.

[super30admin]

Strengths:

• The solutions are correct and efficient, with accurate time and space complexity analysis.
• The code is well-organized and readable, with good use of helper functions.
• Comments and variable names are clear and descriptive.

Areas for Improvement:

• In NQueens.py, the isSafe function could be optimized further by checking only the necessary positions (upper rows, upper left, and upper right) without resetting i and j multiple times. This is a minor optimization but could improve clarity.
• In WordSearch.py, the dfs function could be slightly optimized by returning early if the word is found, which it already does, but the logic could be made more explicit in comments.