Basic Refactoring: Type Annotations, Final & Const Usage

[Marc-R2]

This PR introduces some basic refactoring to improve code readability and maintainability:

• Added type annotations where possible for better static typing
• Replaced variables with final where applicable to ensure immutability
• Used const for constant values (optimize performance)

These changes don't affect the functionality of the package but should improve the overall code quality.

I will continue to break down the larger changes into smaller PRs for easier review and integration.

Thanks!