Missing unit tests and test structure

[MiguelAntonioRS]

Description

The project lacks any testing infrastructure or unit tests for core components like rendering, input handling, or game loop logic.

Suggested solution

Add:

• Basic JUnit test structure
• Tests for essential methods in Game class
• Example test cases for frame rate control or rendering

Motivation

Adding tests improves maintainability and helps contributors ensure their changes don't break existing functionality.