pub fn new(builder: &mut Builder<C>) -> Self {
        DuplexChallengerVariable::<C> {
            sponge_state: core::array::from_fn(|_| builder.eval(C::F::zero())),
            input_buffer: vec![],
            output_buffer: vec![],
        }
    }
Creates a new duplex challenger with the default state.
crates/recursion/circuit/src/challenger.rs