There is a way to organize your functions into a category so it will show up in the “Palette” panel, as well as when you right click to search in a material under a separate header. This helps to organize the functions you create, it is not quite the same as a namespace format you mentioned, but can be useful for organizing groups of functions.
If you want to use the library organizing method, I have included a picture of how it is set up below. Click on the background of the material function so no nodes are selected, and you will see the details panel shown below where you can create a Library category. Just create a category name, and make sure Expose to library is selected and your functions will show up in the category as shown.
Hope that helps!