eth/downloader, eth/protocols/snap: remove healing and genTrie, restructure sync loop for snap/2
eth/protocols/snap: Implement BAL fetching
eth/protocols/snap: create functions for bal verification and apply
eth/downloader,eth/protocols/snap: implement catch-up on pivot
eth/protocols/snap: add tests and fix peer registration for access lists
eth/protocols/snap: add pivot movement integration tests
core, core/state/snapshot: skip snapshot generation after sync completion
eth/protocols/snap: skip new empty accounts in applyAccessList and test
