WR-483012 Add cleaner_question_attempts subplugin

[agaranin]

Summary

• New datacleaner subplugin that deletes old question attempt data (question_usages, question_attempts, question_attempt_steps,
  question_attempt_step_data) based on a configurable age threshold (default: 30 days)
• Uses Moodle's question_engine::delete_questions_usage_by_activities() API for safe cascade deletion with chunked processing (10K usages per
  batch)
• Fast path: when minimum age is 0, truncates all 4 tables directly and cleans only response file metadata (preserves question definition files)
• Sortorder 9 (pre-wash zone, runs before courses cleaner)

Closes #227