feat: add color mixer game

[ShivamMishra1603]

Description

Describe your contribution.

Adds the Color Mixer mini-game under games/chill/color_mixer/game.py.
The game randomly generates two primary colors (red, blue, yellow) and asks the player to guess the mixed result, keeping score over multiple rounds.

Checklist

• My game defines an AUTHOR variable
• My game defines a run() function
• I did NOT add run() at the end of the file
• I did NOT add if __name__ == "__main__"
• I removed any .pyc files
• I removed any .DS_Store files
• The game works correctly when launched from launcher.py

Issue

Closes #95

[Yugo206]

Thanks for the contribution!

The code is clean and easy to follow, and I like the use of a frozenset to handle color combinations regardless of order.

Everything looks good to me. Thanks for contributing!