…disable/enable, and error fields

- Invoice: add customer_external_id, collection_method, status, disabled,
  disabled_at, disabled_by, user_created, errors, edit_history_summary
- Invoice.LineItem/Transaction: add error field
- Invoice: add destroy_all, updateStatus, disable, enable methods
- SubscriptionEvent: add invoice_external_id, disabled, disabled_at,
  disabled_by, user_created fields
- SubscriptionEvent: create/updateWithParams/deleteWithParams now accept
  flat params (union type with envelope style)
- SubscriptionEvent: add disable/enable methods
- Add test cases for all new methods

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>