Allow non-`time`-labelled nodes and edges in `NetworkGroup`
In the create_graph()
function, nodes and edges are treated separately in order to handle the case of static network structure but properties that change in time (for example). The at_time
specifiers are neglected in the case of len(node_cont.coords['time']) == 1
.
This is not compatible with the save_graph
function in Utopia, as this creates non-time-labelled datasets.
Therefore, the data should be considered 'static' when there is no time dimension.