Add a Current Block into preconf contract

[ckartik]

We want to add a currentActiveBlock on ethereum, to ensure that a builder can't post a pre-confirmation after the fact.

[ckartik]

@Man-Jain would love any insight you might have here. Especially if you've got insights into the OP-Stack smart-contracts.

[ckartik]

Also worth noting that these contracts are going to be deployed on our OP-Stack based L2.

[Man-Jain]

Not an expert on the OP stack but there's this contract L1Block which is to be deployed on L2 and is updated with the current L1 block data. You can then query this contract to put a check / modifier on the pre-confirantion function.

https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/src/L2/L1Block.sol#L13 @ckartik