Fixed all issues (1-6) and applied refactoring and encapsulation

[hardip-muliyasiya]

This pull request fixes all the issues and applies refactoring and encapsulation.

• Closes Increase difficulty level as the game proceeds. #1 : Increased difficulty level as the game proceeds.
• Closes Food should not spawn inside snakes body #2 : Ensured food does not spawn inside the snake's body.
• Closes Maintain and update score as the game proceeds #3 : Maintained and updated the score as the game proceeds.
• Closes Spawn poisonous food that snakes needs to avoid. #4 : Spawned poisonous food that the snake needs to avoid.
• Closes Add play/pause functinality in the game #5 : Added play/pause functionality to the game.
• Closes Keep track of top 10 highest scores #6 : Kept track of the top 10 highest scores.
• Fixes bug: Preventing the snake from reversing direction directly.
• Applies refactoring.
• Applies encapsulation.

All updates were committed separately to maintain the individual changes visible.