* Fix `SELECT COUNT` queries when rendering ActiveRecord collections

Fixes #40837

When rendering collections, calling `size` when the collection is an
ActiveRecord relation causes unwanted `SELECT COUNT(*)` queries. This
change ensures the collection is an array before getting the size, and
also loads the relation for any further array inspections.

* Test queries when rendering relation collections

* Add `length` support to partial collection iterator

Allows getting the size of a relation without duplicating records, but
still loads the relation. The length method existence needs to be
checked because you can pass in an `Enumerator`, which does not respond
to `length`.

* Ensure unsubscribed from notifications after tests

[Rafael Mendonça França + aar0nr]