Enable 200ms Flashblocks on a Flashblocks-enabled devnet

Tweak the rbuilder to produce Flashblocks at a 200ms rate.

Observe their stability as compared to the 250ms counterpart over a few days.

Heads up: This issue might potentially branch out into other operational work. For example: spinning up an NVME-backed op-rbuilder in the devnet if the non-NVME setup becomes bottleneck beyond 250ms time.

Start by locating the rbuilder configuration or entry point used by the Flashblocks-enabled devnet, then compare its 200ms behavior with the 250ms counterpart over a few days. Done means the 200ms rate is running and its stability has been observed; investigate NVME-backed op-rbuilder work only if the non-NVME setup becomes a bottleneck.

Written by the indexing model from the issue text.