pub fn columns(&self) -> Vec<Vec<FieldElement<F>>> {
        (0..self.width)
            .map(|col_idx| {
                (0..self.height)
                    .map(|row_idx| self.data[row_idx * self.width + col_idx].clone())
                    .collect()
            })
            .collect()
    }
Returns a vector of vectors of field elements representing the table
columns
crates/provers/stark/src/table.rs