* Somewhat tighten error handling
why:
Zombie state is invoked when the current peer turns out to be useless
for further communication. While there is a chance to further talk
to a peer about another topic (aka healing) after some protocol failure,
it makes no sense to do so after a network problem.
The latter state is explained bu the `peerDegraded` flag that goes
together with the `zombie` state flag. A degraded peer is dropped
immediately.
* Remove `--sync-mode=snapCtx` option, always start snap in recovery mode
why:
No need for a snap sync option without recovery mode, can be achieved
by deleting the database.
* Code cosmetics, typos, prettify logging, debugging helper, etc.
* Split off snap sync sub-mode handler into separate modules
details:
The original `worker.nim` source has become a multiplexer for several
snap sync sub-modes `full` and `snap`. The source modules of the
incarnations of a particular sync sub-mode are places into the
`worker/play` directory.
* Update ticker for snap and full sync logging
* Clean up some function prototypes
why:
Simplify polymorphic prototype variances for easier maintenance.
* Fix fringe condition crash when importing bogus RLP node
why:
Accessing non-list RLP entry as a list causes `Defect`
* Fix left boundary proof at range extractor
why:
Was insufficient. The main problem was that there was no unit test for
the validity of the generated left boundary.
* Handle incomplete left boundary proofs early
why:
Attempt to do it later leads to overly complex code in order to prevent
looping when the same peer repeats to send the same incomplete proof.
Contrary, gaps in the leaf sequence can be handled gracefully with
registering the gaps
* Implement a manual pivot setup mechanism for snap sync
why:
For a test scenario it is convenient to set the pivot to something
lower than the beacon header from the consensus layer. This does not
need rely on any RPC mechanism.
details:
The file containing the pivot specs is specified by the
`--sync-ctrl-file` option. It is regularly parsed for updates.
* Fix calculation error
why:
Prevent from calculating negative square root
