SHA256 recursive circuit

Extend `Sha256Circuit` with `snark-verifier` to trust previously verified hashes. Document the final design back to specification. Determine the effectiveness of this optimization.

### Inputs:
- public `unverified_hashes: Vec<(Vec, U256)>`
- public `truted_hashes: Vec<(Vec, U256)>`
- private `previous_proof` (previous instance of the recursive proof)

### Behavior:
- verify `previous_proof`
- calculate `unverified_hashes` using SHA256 hash function

### Notes:
- for recursion use https://github.com/axiom-crypto/snark-verifier
- for halo2 use https://github.com/privacy-scaling-explorations/halo2.git

### [Spec](https://hackmd.io/@timofey/rJq5Bf5r2)

### References
- https://github.com/privacy-scaling-explorations/zkevm-circuits/blob/main/zkevm-circuits/src/root_circuit.rs
- https://github.com/privacy-scaling-explorations/zkevm-circuits/blob/main/zkevm-circuits/src/root_circuit/aggregation.rs