I recently started working on a plugin that allows you to manage new ready-made classes (you can see it here). But due to some issues that are still unresolved I decided to prepare some classes for it before it was ready and I created some classes including the percentage class, I had some conversations yesterday that made me decide to prepare this class for use and added some features to it, you can see it here and download:
There is more guidance on the main page of the repository and inside the file (with Godot documentation system), but if there are any questions I will be happy to answer, I may also publish a demo of how to use it soon.
I would be happy to try it out!