If you have many project that use many of the same code base you can build a library to share code between the projects. Librarys are just static instances of a stand alone project that your sharing with other projects. When you need to make changes to the library you have to push a new version of the library and then you have to change it from within the project that you are using the library with.
Google Apps Script Github Assistant allows you to sync your extension to github for perment version control of your project. You can pull and push all your code to with very minimal hassel. This extension is fully featured you can have branches and manage what get sync and what doesn’t. Google has a versioning for there libraries but this is only used for allowing other to use the library and you can’t pull down a older version and work on it.
This extension add a dark theme and add the functionality of folder. Its a really nice touch.