funding_rate() :: ExFtx.FundingRate.t()

future_name() :: String.t()

params() :: %{
  optional(:future) => String.t(),
  optional(:start_time) => non_neg_integer(),
  optional(:end_time) => non_neg_integer()
}

result() ::
  {:ok, [funding_rate()]}
  | {:error, :not_found | :parse_result_item | String.t()}