This is a spin-out from the EIP-4844 devnet branch, containing just the Engine API modifications
and nothing else. The newPayloadV3 endpoint won't really work in this version, but we need the
data structures for testing so I'd like to get this in early.
Co-authored-by: Marius van der Wijden <m.vanderwijden@live.de>
This PR moves core/beacon to beacon/engine so that beacon-chain related code has its own top level package which also can house the the beacon lightclient-code.