Function inline_runs_from_markdown 

pub fn inline_runs_from_markdown(text: &str) -> Vec<InlineRun>

Parse a docling-legacy Markdown string into structured InlineRuns for a Node::InlineGroup. Handles the marker set docling emits — ***, **, *, ~~, `, [t](u) — recursively so nested markers combine formatting, and splits plain text on newlines (docling’s <br> / text-node boundaries become separate runs). Underline and sub/superscript have no Markdown representation and therefore never appear via this path.