stream2.rb

class Loader
  def load
    Enumerator.new { |main_enum| stream(main_enum) }
  end

  private

  def stream(main_enum)
    reader = nil
    file_uri.open do |file|
      reader = Zlib::GzipReader.new(file)
      reader.each_line.lazy.drop(1).each do |line|
        main_enum << preprocess_row(line)
      end
    end
  ensure
    reader&.close
  end

  def file_uri
    URI.parse("ftp://user:password@host.com/file.csv.gz")
  end

  def preprocess_row(row)
    row.chomp.gsub('"', "").split(",")
  end
end

building a proper streaming CSV parser, you would actually open an IO object, pass that into CSV.foreach, and then feed each line into the IO

what about CSVs containing quoted newlines, nested quotes, etc?