Optionalhash: OpaqueHash & pvm.WithOpaque<"trie">Protected StaticwithReturns a string identifier of that hash to be used as a key in DB.
Before calling toString the first bit is set to 0, to maintain compatibility
with branch nodes, which have the left subtree stripped out of the first bit
(since it's a branch node identifier).
A version of
NodesDbaugmented with mutating methods.