feature: added difficulty levels to snake game🐍

[siri-004]

📝 Description

This PR fixes the Snake Game loading and initialization issues and introduces difficulty levels for improved gameplay experience.

🚀 Changes Made

• Fixed getSnakeGameHTML function reference issue
• Properly exposed Snake Game functions to global scope
• Resolved addEventListener null errors
• Added difficulty selection support (Easy, Medium, Hard)
• Improved game initialization flow
• Added a Best Score feature to track the highest score achieved during gameplay.

🎯 Impact

The Snake Game now loads correctly without errors and provides customizable gameplay difficulty for users.

🔗 Linked Issue

Closes #412

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📋 Contribution Checklist

• My code strictly adheres to the project guidelines (Standard library only, procedural code, clean spacing).
• I have verified that my files are placed in the correct directory.
• I have tested my changes thoroughly on my local machine.
• I have included interactive emojis and clean console/UI outputs.
• GSSoC 2026: I have been formally assigned to this issue and noted it above.

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[github-actions]

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