feat(node): L2 finality signal handling

[clabby]

Overview

An addition to the actors has to be made in order to watch for L1 finalized block updates, and promote L2 blocks to the finalized label as a result.

This will require the node to hold onto a queue of OpAttributesWithParent (along with the L1 blocks that they were derived from). The op-node does this via the EngineQueue, for reference.