That is, find all nodes connected to node by an outgoing edge.
This function is memorized to avoid making repeated API queries.
Value
A character vector of all nodes in graph connected such that
there is an outgoing edge for node to those nodes. This should
never be empty, as neighborhood() should not be called on nodes
that fail check(), and check() enforces that nodes have out-degree
of at least one. It is critical node names are duplicated in the
output recommend calling unique() if there is any potential for
for that to occur.