CX Reader creates individual attribute values from collection-level attributes

If there is a collection-level network attribute, it should NOT be copied to each subnetwork.

However, current reader always copied collection values into all subnetwork tables.

Start by tracing the CX Reader's handling of collection-level network attributes and compare how values are written to subnetwork tables. Confirm the change by checking that collection-level attributes remain at collection scope and are not duplicated for each subnetwork.

Written by the indexing model from the issue text.