chore: replace the simulated backend with live Geth

[karalabe]

Our simulated backend reimplements/duplicates a lot of API and functional code pointlessly, the origin of which was mostly due to the evolution of Geth:

• 2015: Ship dev mode in ethash
• 2016: Ship abigen and the simulated backend with chain makers (dev mode / ethash unfeasible)
• 2017: Ship Clique enabling a lightweight dev mode

At this point it was "don't touch if it ain't broken". Still, time went on:

• 2022: Ship The Merge, making both ethash/clique unable to follow recent forks

At this point, it "was broken", as the simulated backend cannot enable recent hard forks, so it fails to be usable as a contract testing backend. Solving the issue is not trivial though, because there's nothing to replace it with.

• 2023: Ship a simulated beacon chain and replace dev mode with it

Now we're in a better position, Geth is able to run a self-contained chain that can follow all the latest hard forks. Whilst we could maybe try and mush into a simulated beaconchain into the simulated backend, that would make it duplicate even more code. The alternative proposal is to wrap a dev mode internally inside the simulated backend, which would instantly nuke out all code duplication and have our simulated backend act exactly as a production Geth... because it is... a production Geth.