* 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
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