InMemoryOrderRepository

Implement InMemoryOrderRepository: - nested exception OrderNotFound - save(order) stores a COPY of the order dict (keyed by order['id']) - get(order_id) returns a COPY; unknown id raises OrderNotFound - all() returns a list of copies Graded probe: mutating the dict you received from get() must NOT change repository state — storage leaks through shared references are the classic repository bug.