Report Valid ExecutionStatus only after all stages (#3212)

* Stricter transition check

* EthBackendServer.numberSent was unused

* Take account of PoS blocks in TopSeenHeight

* Report Valid ExecutionStatus only after all stages, not straight in headers

* Print TTD on startup

* No need to check parent.Hash() again

* core: change baseFee into baseFeePerGas in genesis json

* fix typo

Co-authored-by: Martin Holst Swende <martin@swende.se>