v6.0 - Game Engine Upgrade and Quality of Life Improvements

This quality of life upgrade is for long-term stability:

• Upgraded game engine to Unity 6.3, to keep the game current

• Removed unused packages and game assets, updated necessary libraries (e.g. for camera controls and localization) to optimize game build and gameplay

• Fixed minor bugs with background layering

Thanks to anyone who's playing and have a great Xmas!