Use Gradle based build system

[NeRdTheNed]

This PR:

• Re-organises the source code directory structure to fit Gradle conventions.
• Creates a basic build script using Gradle, which handles dependency management and packaging libraries with the built .jar.
• Creates a GitHub Actions workflow to build the project whenever the "main" branch of the GitHub repository is pushed to, or receives a pull request. Any successfully built files are uploaded and attached to the workflow run.
• Updates the README with relevant information about building with this new system.

[xhendrikg]

I get an error :( do you have discord?

[xhendrikg]

I get an error :( do you have discord?

and how even use ur PR lol