why:
It is not safe in general to recycle vertex IDs while the `RocksDb`
cache has `VertexID` rather than `RootedVertexID` where the former
type seems preferable.
In some fringe cases one might remove a vertex with key `(root1,vid)`
and insert another vertex with key `(root2,vid)` while re-using the
vertex ID `vid`. Without knowledge of `root1` and `root2`, the LRU
cache will return the same vertex for `(root2,vid)` also for
`(root1,vid)`.
* Implement partial trees
why:
This is currently needed for unit tests to pre-load the database
with test data similar to `proof` node pre-load.
The basic features for `snap-sync` boundary proofs are available
as well for future use. What is missing is the final proof verification
and a complete storage data load/merge function (stub is available.)
* Cosmetics, clean up
Jordan Hrycaj