As shown in Modularising CPI Groovy scripts using POGO | SAP Blogs classes that are in other scripts are available by importing them with:
import src.main.resources.script.ClassName
They just sitting in:

What happens when I put such a class in a separate package? What is the import path then?

I tried to move the class directly to a file in Common Script Collection and the import doesn't work. When the class is in the Local file the import works.