Plan out Rollup Boost integration

[Thegaram]

The most convenient approach to integrating Phylax into the Scroll sequencer is to tap into the block building process via something like Rollup Boost. We should evaluate what needs to be changed or added so that we can support this external block builder pattern in a safe and performant way.

Note: We do not need to support Rollup Boost exactly (i.e. no need to be compatible with OP's setup), just something similar.

Sources:

• https://rollup-boost.flashbots.net
• https://github.com/ethereum-optimism/design-docs/blob/main/protocol/external-block-production.md
• https://github.com/flashbots/rollup-boost
• https://docs.phylax.systems/credible/architecture#rollup-boost-pattern-op-stack