Function format_assertion_rows_for_junit 

fn format_assertion_rows_for_junit(
    columns: &[String],
    missing: &[BTreeMap<String, String>],
    unexpected: &[BTreeMap<String, String>],
) -> String

Formats structured assertion data into plain-text for JUnit XML output.

Renders each row as column_name=value pairs, grouped by status (MISSING / UNEXPECTED), making failures easy to diagnose from CI reports.