fix authorlist to use native node implementation

this MR fixes the authorlist directive to be compatible with myst_parser. we now create the nodes natively without the inline parsing. How the footnode nodes are created has been taken from the implementation in the myst_parser library.

note that due to how myst_parser handles footnotes, you will still see warnings like this:

WARNING: No footnote definitions found for label: 'affil0' [myst.footnote]

these warnings can be savely ignored

@bjoern.sass it would be great if you could confirm that this works and merge this MR

closes #1 (closed)