add check_consensus_blob_count task

[zexoverz]

This is the target/max half of #88. The task watches proposed blocks and checks the blob count against the chain's target or max, reading both numbers from the execution client's eth_config instead of a number written into the playbook, because the consensus config only publishes MAX_BLOBS_PER_BLOCK and carries no target at all. A block over max aborts rather than counting as a miss, since that is a violation and not just an underfilled block.

I left the pre-propose pool snapshot out until you answer the question in the issue, so this does not guess between a lead-time knob on this task and a separate recorder task. I also made it a new task rather than more flags on check_consensus_block_proposals, since the limits come from an execution RPC and that check is consensus only, but it folds in easily if you would rather have it there.

[zexoverz]

Could someone approve the workflow run? It is sitting at action_required, so CI has not run on this one yet.