Cross reference on nbdev

Quarto [cross referencing](https://quarto.org/docs/authoring/cross-references.html#code-listings) is very uselful when generating docs. I was able to use this feature with nbdev by using raw cells.

It would awesome to have a nbdev directive to reference a code cell in a markdown cell, for example:


Right now I'm using Quarto syntax on nbdev raw cells containing python code (see images below) but it can be a little limited since I can't test the code used on the raw cell.