Improve list performance when REST APIs return data in the query

Changing the title of this to be clearer.

I'm seeing this issue as well with 📌 Use external_entities to declare Unomi types as Drupal entities Active -- making one call for each row of the list is really slow.

> For a listing to perform a query & have the full objects returned in the same response: this is something the storage client could build in, possibly by using the MemoryCache (https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Cache%21M...).

In my case that's not possible, as the Unomi REST API returns metadata only from a query. It's not full entities, but it's enough data to show a useful list.

So in my case there's a need for the entity query to return more than just IDs -- which goes completely against the grain of the Drupal entity system.