Defer code loading when active record is properly loaded

[benoittgt]

This is well known issue. We should prefer to load code that reference active record only when it's AR is already loaded. It can break other gems initializing process like https://github.com/thoughtbot/factory_bot_rails/pull/432

Related:

• https://github.com/rails/rails/issues/46567
• https://github.com/paper-trail-gem/paper_trail/commit/fc6c5f69410f1b79e617610d522dbedfa4f04f7f (inspiration)
• https://github.com/thoughtbot/factory_bot_rails/pull/432

Fix: https://github.com/DatabaseCleaner/database_cleaner-active_record/issues/89

[benoittgt]

Closing in favor of https://github.com/DatabaseCleaner/database_cleaner-active_record/pull/91