experimental: create new payload from EL error hints

[merklefruit]

Warning

highly cursed code ahead!

We attempt to build a valid execution payload by sending a template to the engine API and infer hints on some stateful components such as state root, gas used and logs bloom.

This approach is highly unstable and not meant to work on a production setup but rather as a proof of concept for a remote block builder without having to either:

• fork execution client code
• access the state database directly
• simulate transactions locally

Implementation

1. create a payload template with the given transactions and context from the latest execution block
2. repeatedly call the EngineHinter to produce hints one at a time until the payload is valid
3. build a locally-signed SignedBuilderBid submission object with a local BLS key