Store rollup node ArbSys block numbers if on an Arbitrum host chain

[PlasmaPower]

This lets the nitro node do efficient log queries for the node creation event, even when running an L3.

[gzeoneth]

We can also change createdAtBlock to return L1/L2 block number based on if it is a L2/L3 to optimize storage, createdAtBlock it is currently used in

1. off-chain event lookup
2. validatorAfk check (which should be replaced by deadlineBlock instead)
3. time delta of minimumAssertionPeriod (can be removed in new protocol)

but LGTM otherwise

[PlasmaPower]

Yeah, I had the same thought about the validatorAfk check but didn't realize the minimumAssertionPeriod is getting removed in the new challenge protocol. That's good to hear, but until then I think it'd make sense to merge this as-is.

[gzeoneth]

Yeah, I had the same thought about the validatorAfk check but didn't realize the minimumAssertionPeriod is getting removed in the new challenge protocol. That's good to hear, but until then I think it'd make sense to merge this as-is.

because there is only 1 deterministic assertion to be made, so I think we don't need that anymore; not sure about potential dos tho