* Add state root to node steps path register `RPath` or `XPath`
why:
Typically, the first node in the path register is the state root. There
are occasions, when the path register is empty (i.e. there are no node
references) which typically applies to a zero node key.
In order to find the next node key greater than zero, the state root is
is needed which is now part of the `RPath` or `XPath` data types.
* Extracted hexary tree debugging functions into separate files
* Update empty path fringe case for left/right node neighbour
why:
When starting at zero, the node steps path register would be empty. So
will any path that is before the fist non-zero link of a state root (if
it is a `Branch` node.)
The `hexaryNearbyRight()` or `hexaryNearbyLeft()` function required a
non-zero node steps path register. Now the first node is to be advanced
starting at the first state root link if necessary.
* Simplify/reorg neighbour node finder
why:
There was too mach code repetition for the cases
* persistent or in-memory database
* left or right move
details:
Most algorithms apply for persistent and in-memory alike. Using
templates/generic functions most of these algorithms can be stated
in a unified way
* Update storage slots snap/1 handler
details:
Minor changes to be more debugging friendly.
* Fix detection of full database for snap sync
* Docu: Snap sync test & debugging scenario
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