Add number guessing game with input validation and guess counter

[chmodgaurav]

Description

Adds NUMBER_GUESSING.py, an interactive number guessing game. The user
specifies an upper bound, the program picks a random secret number within
that range, and the user guesses repeatedly until correct. The game
validates input (rejects non-integers and out-of-range guesses) and
reports the total number of guesses taken at the end. Also updates
README.md to list the new script.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code cleanup/refactoring

Related Issues

Closes #(issue number)

Testing

• Manual testing
• Added automated tests
• Existing tests pass

Checklist

• My code follows the project's code style
• I have commented my code, particularly in hard-to-understand areas
• I have updated the README.md if needed
• My changes generate no new warnings
• I have tested my code locally
• New and existing tests pass with my changes