* eth/downloader: implement beacon sync
* eth/downloader: fix a crash if the beacon chain is reduced in length
* eth/downloader: fix beacon sync start/stop thrashing data race
* eth/downloader: use a non-nil pivot even in degenerate sync requests
* eth/downloader: don't touch internal state on beacon Head retrieval
* eth/downloader: fix spelling mistakes
* eth/downloader: fix some typos
* eth: integrate legacy/beacon sync switchover and UX
* eth: handle UX wise being stuck on post-merge TTD
* core, eth: integrate the beacon client with the beacon sync
* eth/catalyst: make some warning messages nicer
* eth/downloader: remove Ethereum 1&2 notions in favor of merge
* core/beacon, eth: clean up engine API returns a bit
* eth/downloader: add skeleton extension tests
* eth/catalyst: keep non-kiln spec, handle mining on ttd
* eth/downloader: add beacon header retrieval tests
* eth: fixed spelling, commented failing tests out
* eth/downloader: review fixes
* eth/downloader: drop peers failing to deliver beacon headers
* core/rawdb: track beacon sync data in db inspect
* eth: fix review concerns
* internal/web3ext: nit
Co-authored-by: Marius van der Wijden <m.vanderwijden@live.de>
