added snake game

[vivek2004-sec]

Description

This PR adds a classic Snake game implementation using tkinter. The player controls a snake using the arrow keys, guiding it around a canvas to eat randomly-placed food. Each time the snake eats food, it grows longer and the score increases; the game ends if the snake collides with the canvas walls or its own body.
Core components:

Snake class — initializes the snake's starting body segments (as coordinates and canvas rectangles)
Food class — spawns food at a random grid-aligned position on the canvas
next_turn() — the main game loop: moves the snake each tick based on current direction, checks for food collision (grow + increment score) or normal movement (remove tail segment), checks for game-ending collisions, and re-schedules itself via window.after()
change_direction() — handles arrow key input, with a safeguard preventing the snake from reversing directly into itself (e.g., can't go left while moving right)
check_collisions() — detects wall collisions and self-collisions
game_over() — clears the canvas and displays a "GAME OVER" message
The game window is also centered on the screen at launch using screen/window dimension calculations.
Problem it solves: Adds a complete, playable, classic arcade game to the repository as an example of tkinter canvas manipulation, game loops using window.after(), and simple 2D collision detection — useful as a learning reference for GUI-based game development in Python.

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

Please describe the tests you've run to verify your changes:

• 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

Screenshots (if applicable)

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