Backend fields not yet modeled here are passed through by the transform.
OptionaldateWindow key/date of this entry (historical range results).
OptionalisTrue when the param is cumulative (e.g. an energy meter).
OptionalparameterBackend parameter identity, "<node_id>.<key>.<data_type>".
Aggregates keyed by window type.
One aggregate entry (per parameter, per window/date).