* Simplify pivot update
why:
No need to fetch the pivot header from the network when it can be
be made available in the ivot cache
also:
Keep `txPool` update disabled while syncing
* Cosmetics, tune down some logging noise
* Support `snap/1` without `eth/6?`
why:
Eth is not needed here.
* Snap is an (optional) extension of `eth`
so:
It it must be supported somehow. Nevertheless it will be currently
unused in the snap syncer.
* Register external beacon stream header
why:
This will be used to sync the peers against.
* Update total coverage book-keeping for 100% roll-over
details:
Provide commonly available/used function
* Replace best pivot by beacon stream tracker
details:
Beacon stream header cache will be updated by external chain monitor via
RPC. This cached header will then be used to sync the pivot.
Jordan Hrycaj
jangko