Function find_notes_session 

pub fn find_notes_session(document: &Document) -> Option<&Session>

Finds the Notes/Footnotes session in a document.

A session is considered a Notes session if:

1. Its title is “Notes” or “Footnotes” (case-insensitive), OR
2. It’s the last session and contains only list items (implicit notes section)

Returns None if no Notes session is found.