message: use slices instead of vecs
diff: @@ -30,7 +30,7 @@ pub fn init_cell<F: PrimeField>(
  offset: usize,
  row: usize,
  col: usize,
  - layout: &Vec<[Box<dyn WitnessCell<F>>; COLUMNS]>,
  + layout: &[[Box<dyn WitnessCell<F>>; COLUMNS]],
  variables: &Variables<F>,
  ) {
  witness[col][row + offset] = layout[row][col].value(witness, variables);
  @@ -41,7 +41,7 @@ pub fn init_row<F: PrimeField>(
  witness: &mut [Vec<F>; COLUMNS],
  offset: usize,
  row: usize,
  - layout: &Vec<[Box<dyn WitnessCell<F>>; COLUMNS]>,
  + layout: &[[Box<dyn WitnessCell<F>>; COLUMNS]],
  variables: &Variables<F>,
  ) {
  for col in 0..COLUMNS {
  @@ -53,7 +53,7 @@ pub fn init_row<F: PrimeField>(
  pub fn init<F: PrimeField>(
  witness: &mut [Vec<F>; COLUMNS],
  offset: usize,
  - layout: &Vec<[Box<dyn WitnessCell<F>>; COLUMNS]>,
  + layout: &[[Box<dyn WitnessCell<F>>; COLUMNS]],
  variables: &Variables<F>,
  ) {
  for row in 0..layout.len() {
  