feat: add wip-1004 subsidy enforcement via handler hooks

[kilianglas]

Summary

Adds WIP-1004, an alternative realization of subsidy enforcement to WIP-1003. Scoped to WIP-1001 0x1D transactions and realized through three op-revm Handler hook overrides. On OP-Stack, the subsidy is a no-op for the ETH ledger — the caller is not pre-charged for the subsidized fraction and the corresponding fee-vault credits in reward_beneficiary are skipped. No treasury, no minting; the per-nullifier WIP-1002 budget caps the operator's forgone fee revenue.

A 0x1D transaction whose framed sender is authorized under a WIP-1002 nullifier with sufficient remaining budget can be sent with zero ETH held by the sender — base fee, priority fee, L1 data fee, and operator fee are all subsidisable.

Trade-offs vs WIP-1003

• No chain-wide baseFeePerGas = 0 pinning; protocol fee market untouched.
• No virtual fee market or VirtualFeeOracle.
• No per-block builder-owned subsidy-accounting transaction.
• No mandated wallet RPC overrides.
• The gasLimit vs gasUsed ambiguity in WIP-1003 §6 is resolved by construction: final settlement happens in reimburse_caller once gas_used is known.
• Subsidy covers the full effective gas price plus L1 / operator fees; WIP-1003 covers only the (virtual) base fee.

Cost: scope is 0x1D only. WIP-1003 nominally applies to all tx types, though WIP-1002 authorization is keyed to WIP-1001 accounts so subsidy-eligible traffic is in practice a subset of 0x1D under either proposal.

WIP-1001 / WIP-1002 coordination needed

• WIP-1001's pre-validation balance check ("worst-case payload gas charge + MIN_VALIDATION_FAILURE_FEE") must be made subsidy-aware so a 0-ETH sender can pass it.
• WIP-1002's consumeBudget interface needs a wei-amount form — the existing consumeBudget(nullifier, gasUsed, baseFee) signature can't express a generic subsidy amount once priority/L1/operator fees are in scope.

The two are mutually exclusive realizations of Subsidy Enforcement; only one can ship.

Test plan

• Spec review by core team
• Decide between WIP-1003 and WIP-1004
• Cross-check pre-charge / post-refund invariants with the WIP-1002 consumption interface change
• Confirm the OP-Stack centralized-sequencer assumption documented in Security Considerations

[0xOsiris]

Can you change to wip-1005 please