Add a new game mode called "Speed Boost Mode" where eating an apple grants the snake a temporary speed boost.
- When enabled, eating an apple activates a 2x speed boost for 3 seconds
- The boost is temporary and automatically expires
- Multiple apple pickups refresh the boost timer (don't stack)
- Adds risk/reward: faster movement = harder to control
Add a new game mode called "Speed Boost Mode" where eating an apple grants the snake a temporary speed boost.