Function build_line_text_runs 

pub fn build_line_text_runs(
    line_text: &str,
    spans: &[StyleSpan],
    selection_line_range: Option<(usize, usize)>,
    fonts: &RunFonts<'_>,
    theme: &EditorTheme,
    is_code_block: bool,
    is_checked_task: bool,
) -> Vec<TextRun>

Builds styled text runs for a single line by blending syntax spans and active selection.