GfmNodeRenderer
Node renderer that converts the AST to GitHub Flavored Markdown (GFM).
Standard CommonMark and GFM constructs are emitted with their native syntax (# headings, **strong**, fenced code blocks, GFM tables, task list items, ...). Quarkdown-specific nodes without a direct Markdown equivalent degrade gracefully: their inner content is emitted where meaningful, while purely presentational or document-structural nodes render as empty strings.