improve on constant folding in multicircuits

- because they have more context, fold constants in the monads
- if constant folding results in an already-existing sub-circuit, that
    sub-circuit is used instead of the newly created one
- rename `InputIndicator`'s “*_row” to “*_column”
- re-arrange the expression of some constraints to de-duplicate
    sub-circuits (Processor Table only)
- perform constant folding just after the construction of the
    multicircuit instead of in the compiler

Co-authored-by: sword-smith <thor@neptune.cash>

constraint-evaluation-generator/src/main.rs

@@ -280,9 +280,6 @@ fn turn_circuits_into_degree_bounds_string<II: InputIndicator>(
 fn turn_circuits_into_string<II: InputIndicator>(
     constraint_circuits: &mut [ConstraintCircuit<II>],
 ) -> String {
-    // Delete redundant nodes
-    ConstraintCircuit::constant_folding(&mut constraint_circuits.iter_mut().collect_vec());
-
     // Assert that all node IDs are unique (sanity check)
     ConstraintCircuit::assert_has_unique_ids(constraint_circuits);
 
@@ -445,7 +442,7 @@ fn is_bfield_element<II: InputIndicator>(circuit: &ConstraintCircuit<II>) -> boo
     match &circuit.expression {
         CircuitExpression::XConstant(_) => false,
         CircuitExpression::BConstant(_) => true,
-        CircuitExpression::Input(indicator) => indicator.is_base_table_row(),
+        CircuitExpression::Input(indicator) => indicator.is_base_table_column(),
         CircuitExpression::Challenge(_) => false,
         CircuitExpression::BinaryOperation(_, lhs, rhs) => {
             is_bfield_element(&lhs.as_ref().borrow()) && is_bfield_element(&rhs.as_ref().borrow())