Add automatic entity cleanup tracking for scenarios

[AlexSkrypnyk]

Summary

Track entities created during a scenario and delete them at teardown, with an opt-out tag.

Details

Add an opt-in mechanism that tracks every entity created during a scenario and deletes them (in reverse order) at scenario end, with a tag to bypass cleanup for specific types. This keeps a test database clean across long suites and prevents cross-scenario contamination from leftover content, users, or files.

Proposed behaviour

• Record entities created through the library's creation steps during a scenario.
• Delete tracked entities in reverse creation order in an @AfterScenario hook.
• Provide a tag to bypass cleanup for named entity types.

Acceptance criteria

• New trait, or shared behaviour, under src/Drupal/.
• Cleanup runs in reverse creation order and tolerates already-deleted entities.
• The bypass tag is documented and honoured.
• Interoperates with the base extension's own cleanup without double-deleting.
• BDD coverage proving created entities are gone after the scenario.
• STEPS.md regenerated via ahoy update-docs if steps are added.