feat(bench): add attack_replay benchmark

[vincent-k2026]

Summary

Adds attack_replay, a hermetic regression benchmark that replays a real MegaETH mainnet attack contract deployment through MegaEvm.

The fixture is a self-contained ~64 KB JSON snapshot captured via debug_traceCall + prestateTracer (diffMode=false) at a fixed block:

• tx: caller / nonce / gas / value / 17 KB initcode / chain_id
• prestate (11 accounts): 4 proxy contracts at 0x4200..., 1 ERC-20 with code + 10 storage slots, the caller, and 5 supporting storage contracts
• block env: number / timestamp / basefee / gas_limit / beneficiary / mix_hash

Bench arms

Three arms on the same in-memory state:

arm	typical wall time	engine
attack_replay/equivalence	~1.15 ms	MegaSpecId::EQUIVALENCE
attack_replay/mini_rex	~35.9 ms	MegaSpecId::MINI_REX
attack_replay/pure_revm	~1.10 ms	vanilla revm (Context::mainnet) baseline

Both mega-evm specs execute the exact same 205,951 opcodes and deploy the same 582-byte runtime. The ~30x gap between EQUIVALENCE and MINI_REX isolates the cost of the multi-dimensional AdditionalLimit accounting (quadratic LOG / compute / storage / data / KV buckets) that MINI_REX enables.

The pure_revm arm is a self-check: it should land near the EQUIVALENCE arm, confirming the bench is honest and not short-circuiting.

Why this bench

Numbers correlate directly with production: the mini_rex arm matches the sequencer-monitor's observed ~33 ms inside api.inspect(...) for this exact transaction, making the bench a stable, reproducible target for any limit-tracker / hot-path optimization (e.g. caching net_usage in FrameLimitTracker).

Sanity checks

Run before criterion warm-up:

• Asserts ExecutionResult::Success variant + reports deployed code length + addr + accounts/slots touched.
• Counts opcode steps via a minimal OpcodeCounter inspector and asserts steps >= MIN_EXPECTED_OPCODE_STEPS (100,000). Any future setup mistake that silently short-circuits tx validation will fail the bench loudly instead of producing artificially fast numbers.

Test plan

• cargo bench --bench attack_replay -p mega-evm --no-run builds clean
• cargo +nightly fmt --check -p mega-evm clean
• cargo clippy --bench attack_replay -p mega-evm 0 warnings
• cargo bench --bench attack_replay -p mega-evm -- --quick runs, all sanity assertions pass, numbers as expected