feat: add ChainSpec AT to EngineTypes

[klkvr]

Currently we use concrete chainspec on EngineTypes, we need to change that to make it possible to make engine generic over chainspec.

This could be approached differently with a generic on EngineTypes — I don't have strong opinion here, though adding it as a generic would require additional generic on engine types which I think would be nice to avoid

[emhane]

seems a bit double up, like an indicator we need to take a step back, and revise the overall design, make a dependency graph. what's the complete list of type that need chainspec associated type? does payload builder need it too for example?