t() :: %ExFtx.Account{
  backstop_provider: boolean(),
  collateral: number(),
  free_collateral: number(),
  initial_margin_requirement: number(),
  leverage: number(),
  liquidating: boolean(),
  maintenance_margin_requirement: number(),
  maker_fee: number(),
  margin_fraction: number(),
  open_margin_fraction: number(),
  positions: list(),
  taker_fee: number(),
  total_account_value: number(),
  total_position_size: number(),
  username: String.t()
}