Add 2D Space Shooter Prototype and Refactor Overlord into a Package

[yuji-teoi]

This pull request introduces two main changes:

• Addition of a new game: a 2D space shooter with independent code, separate from the platformer and top-down games. This game uses Overlord to generate its game content.
• Refactor of the Overlord module: the module has been converted into a package, with the required files and properly named folders.

This pull request also includes prefabs and sprites used by the space shooter.

Notes:

• The game is a prototype and may be improved in future iterations.
• The main objective of this game is to serve as a tutorial base, demonstrating how Overlord can be used to generate content for a new game.