/// Incremental parser result for one pushed chunk (or final flush).#[derive(Debug, Clone, PartialEq, Eq)]pub struct StreamTextChunk<T> {    /// Text safe to render immediately.    pub visible_text: String,    /// Hidden payloads extracted from the chunk.    pub extracted: Vec<T>,}impl<T> Default for StreamTextChunk<T> {    fn default() -> Self {        Self {            visible_text: String::new(),            extracted: Vec::new(),        }    }}impl<T> StreamTextChunk<T> {    /// Returns true when no visible text or extracted payloads were produced.    pub fn is_empty(&self) -> bool {        self.visible_text.is_empty() && self.extracted.is_empty()    }}/// Trait for parsers that consume streamed text and emit visible text plus extracted payloads.pub trait StreamTextParser {    /// Payload extracted by this parser (for example a citation body).    type Extracted;    /// Feed a new text chunk.    fn push_str(&mut self, chunk: &str) -> StreamTextChunk<Self::Extracted>;    /// Flush any buffered state at end-of-stream (or end-of-item).    fn finish(&mut self) -> StreamTextChunk<Self::Extracted>;}