pub fn new_constant(&mut self, value: FE<F>) -> Variable {
        let constant = self.new_variable();
        self.add_constraint(Constraint {
            constraint_type: ConstraintType {
                ql: -FE::one(),
                qr: FE::zero(),
                qm: FE::zero(),
                qo: FE::zero(),
                qc: value,
            },
            l: constant,
            r: self.null_variable(),
            o: self.null_variable(),
            hint: None,
        });
        constant
    }
Returns a new variable `w` constrained to take the value `value`.
crates/provers/plonk/src/constraint_system/types.rs