list_senders now excludes system mailboxes by default
Unscoped list_senders calls were counting messages sitting in Deleted Messages, Junk, Sent, and Drafts — making sender counts misleading after a cleanup.
Default behaviour now excludes those four mailboxes. Pass include_system_mailboxes: true to restore the old behaviour. When mailbox is specified the exclusion is ignored (it scopes to exactly what you asked for).