Make it possible to use the playground for interactive docs

It would be awesome to have a version of the playground which we can embed in documentation and/or blog posts to have interactive snippets.

This is similar in spirit to what @JeffersGlass showed in his excellent pycon talk, with a twist: I think that in his talk, Jeff uses the standard py-editor component, while for spy we probably cannot (because the standard py-editor automatically executes the code with micropython/pyodide, while what we want is to save the content to a virtual file and call the spy cli).