* Remove TotalDifficulty stage
* Introduce FeedHeaderFuncType
* Some TODOs
* Don't gossip PoS headers
* FeedHeaderPoS
* Call header.Hash once
* Use FeedHeaderPoS for to write PoS header
* Support errors in EngineExecutePayloadV1
* useExternalTx boilerplate
* Call VerifyHeader on PoS header
* latestValidHash must be nil when status is SYNCING
* fixCanonicalChain instead of canonicalHeadersCollector
* engine.VerifyHeader + FeedHeaderPoS as headerLoadFunc
* fix daemon
Co-authored-by: Giulio Rebuffo <giulio.rebuffo@gmail.com>
* added download channel to stage headers
* added direct execution
* now channel of headers rather than bodies
* simplifications
* fixed ttd headerForward
* garbage removed
* added some more stepping stones
* better transition
* covered edge case
* added names to returned values
* clean