@type t() :: %ExtFit.Record.FitData{
  __chunk__: ExtFit.Chunk.t(),
  def_mesg: nil | struct(),
  fields: [ExtFit.Types.FieldData.t()],
  is_developer_data: boolean(),
  local_mesg_num: non_neg_integer(),
  time_offset: non_neg_integer()
}