onlyworlds 0.4.0

• A retry that meets its own first try still running now waits and replays (keel #307, D105). After a timeout the client resends with the same Idempotency-Key; if the first request is still running, keel answers 409 idempotency_in_flight with Retry-After: 1. The retry policy now retries that 409 (and only that one), so create and bulk get the first answer's replay instead of an error. ApiError.is_idempotency_in_flight names it when the retries run out.