Produce executed block at the end of flashblock building process

When building flashblocks we need to ensure that produced block will be stored in cache, and when newPayload arrived it would be fetched from memory.
There is no way to guarantee number of flashblocks that would be used during block building (because it greatly affected by latency to rollup-boost) so we should produce executed block after every flashblock and store this executed block in cache
Here's the reference implementation for sending in op-rbuilder (https://github.com/flashbots/op-rbuilder/pull/229) and this is code reference for creating executed block (https://github.com/flashbots/op-rbuilder/blob/fa9924e2fff889862b968e76cacf9f284f9f6e37/crates/op-rbuilder/src/builders/flashblocks/payload.rs#L1035)