[FEAT] Implement "Mirrored" Game Mode

[otaviobia]

Mirrored Game Mode

This is an umbrella issue for the implementation of the "Mirrored" game mode, as described in next_steps.md.

Game Mode Description

In this game mode, there are 2 snakes.

• The snakes move in opposite directions of each other (this creates the mirrored effect)
• If the snakes collide with each other the player loses
• When any of them eat food they both increase in size
• The snakes have different colors

Suggested Sub-Issues

• [FEAT] Add "Mirrored" game mode option to UI

• [FEAT] Implement collision rules for Mirrored mode

• [FEAT] Implement mirrored growth and scoring

Some of them could potentially be broken into even more sub-issues, feel free to discuss this below.