Export on-chain verifier

[rpalakkal]

This involves adding two new functions to halo2-wasm/src/lib.rs:

1. gen_evm_proof to generate a proof with a Keccak transcript instead of a Poseidon transcript
   https://github.com/axiom-crypto/snark-verifier/blob/0b4f1a46a23f0dd06702d71af3da760141f5a347/snark-verifier-sdk/src/evm.rs#L36

2. gen_evm_verifier_shplonk to export a verifier that takes an evm_proof
   https://github.com/axiom-crypto/snark-verifier/blob/0b4f1a46a23f0dd06702d71af3da760141f5a347/snark-verifier-sdk/src/evm.rs#L168C8-L168C32

Once this is added, we should add two new export options to halo2-repl