feat(l1): snap sync overhaul

[fmoletta]

Motivation
This PR introduces the following upgrades for snap-sync:

• Use DB-persisted checkpoints so we can persist the sync progress throughout restarts & cycles
• Stop ForckChoices & NewPayloads being applied while syncing
• Improved handling of stale pivot during sub-processes
• Improved handling of pending requests when aborting due to stale pivot
• Fetching of large storage tries (that don't fit in a single range request)
• Safer (but a bit slower) healing that can be restarted
• Faster storage fetching (multiple parallel fetches)

And also simplifies it by removing the following logic:

• No longer downloads bodies and receipts for blocks before the pivot during snap sync (WARNING: this goes against the spec but shouldn't be a problem for the time being)
• Removes restart from latest block when latest - 64 becomes stale. (By this point it is more effective to wait for the next fork choice update)
• Periodically shows state sync progress

Description

• Stores the last downloaded block's hash in the DB during snap sync to serve as a checkpoint if the sync is aborted halfway (common case when syncing from genesis). This checkpoint is cleared upon succesful snap sync.
• No longer fetches receipts or block bodies past the pivot block during snap sync
• Add method sync_status which returns an enum with the current sync status (either Inactive, Active or Pending) and uses it in the ForkChoiceUpdate & NewPayload engine rpc endpoints so that we don't apply their logic during an active or pending sync.
• Fetcher process now identify stale pivots and remain passive until they receive the end signal
• Fetcher processes now return their current queue upon return so that it can be persisted into the next cycle
• Stores the latest state root during state sync and healing as a checkpoint
• Stores the last fetched key during state sync as a checkpoint
• Healing no longer stores the nodes received via p2p, it instead inserts the leaf values and rebuilds it to avoid trie corruption between restarts.
• The current progress percentage and estimated time to finish is periodically reported during state sync
  Misc:
• Replaces some noisy unwraps in networking module with errors
• Applies annotated hacky fixes for problems reported in bug(l1): connection attempt on already connected peer due to revalidation #1684 bug(l1): wrong logic when validating peer ForkID #1685 & bug(l1): peer connection broken due to failure to add transaction to mempool before sync #1686

Closes None

Closes #issue_number