Function insert_test_data_sql 

pub fn insert_test_data_sql(
    table: &str,
    columns: &[&str],
    values: &[&str],
) -> String

Generate an INSERT statement for test data.

Values are inserted as raw SQL expressions (e.g., 'Alice', NOW()), so they are NOT parameterised. Table and column names are properly quoted via reinhardt_query::Iden.