feat: update zkboost usage

[han0110]

ethereum/consensus-specs#5639 proposes to simplify EIP-8025 by moving proof generation out of the spec, into a prover (e.g. zkboost) that runs as middleware between the CL and the EL. The prover observes engine_newPayload, forwards the request to the EL, and triggers proof generation after a VALID response. zkboost forwards it as engine_newPayloadWithWitness with the arguments unchanged, so that it gets the execution witness.

Once a proof is ready, zkboost signs it as a validator and submits the signed execution proof envelope back to the CL through POST /eth/v1/beacon/execution_proofs (proposed in ethereum/beacon-APIs#569). The CL then verifies, stores, and gossips it.

Proof verification is now embedded in the CL, so zkboost no longer serves a proof verification API. As a side effect, we can no longer test with mock proofs. As a workaround, we prove a mock guest program that has exactly the same input/output as the actual guest program but skips the verification inside, and override the verification key of the CL. This way a single GPU generates proofs fast enough to keep a proof-only CL synced (see the 1gpu_zkvm_with_mock_guest.yaml example).

Changes:

• Run each zkboost instance as the Engine API middleware of exactly one participant, which sets --execution-endpoint=http://<instance>:3000 and --proof-engine in cl_extra_params, and sign proofs with one validator keystore of that participant
• Document --proof-engine (built-in verification keys) and --proof-engine=<path> (custom verification keys, via extra_files and cl_extra_mounts) for a proof-only CL without an EL
• Remove zkVM kinds mock, external, and verifier, allow ere to connect to a running ere-server with endpoint, and add cluster to connect to a ZisK or OpenVM proving cluster
• Replace 1gpu_zkvm.yaml with 1gpu_zkvm_with_mock_guest.yaml, update 8gpu_zkvm.yaml and zkboost.yaml, and remove the verifier examples
• Remove the assertoor zkboost JSON test, and update the zkboost metrics test
• Update the Grafana dashboards of zkboost and Lighthouse

A sibling PR for the new EIP-8025 changes is ethpandaops/dora#881.

Pinging @frisitano for visibility.

[frisitano]

Added some comments inline regarding CPU proving.