pub fn crypto_setup_key(self) -> Self {
        if self.stage == ProvingStage::NodeAggregation {
            return Self {
                circuit_id: 2,
                stage: ProvingStage::NodeAggregation,
            };
        }

        self
    }
Returns the crypto version of the setup key.

Setup key is overloaded in our system. On one hand, it is used as identifier for figuring out which type of proofs are ready.
On the other hand, it is also a setup key from prover perspective.
The 2 overlap on all aggregation rounds, but NodeAggregation.
There's only 1 node key and that belongs to circuit 2.
prover/crates/lib/prover_fri_types/src/lib.rs