We want to allow setting references as public

The constant is written as O(1) not O(C)

Calling .include? on Set is O(1)

Not relevant comment, attributes is callable multiple times now

Add ApplicationRecordLite that is for holding is and class of AR.
ActiveRecord object are to huge and we need a query to obtain them,
in most cases we have a class and id, which is just enough
to fil la relation. No need to go to db.

Collect attribute_references and use them for db strategy.
So we are able to load a relation fro ma db without making a
sql query, wrapping it to ApplicationRecordLite.

Extract InitDataHelper so it's reusable in other specs

Spec testing a db_find_strategy with :key poiting to relation

Autofix rubocop issues

Fix a polymorphic relation loading

Test a polymorphic relation is obtained via :key

Clean up a spec to only use a needed ICs

Look for foreign_key only in belongs_to relations, we would get
a confusing trying to assign to another relation.

Check for allowed strategies and raise exception with a list of
allowed

A complex interconnection spec

Enhance specs and run them for both DB strategies

Autofix rubocop issues

Rename ApplicationRecordLite to ApplicationRecordReference, as
it shows the purpose much better.