In RowBinary raise if `:datetime` is before unix

[ruslandoga]

# in Ch.RowBinary
def encode(:datetime, %NaiveDateTime{} = naive) do
  {seconds, _micros} = NaiveDateTime.to_gregorian_seconds(naive)
  epoch_seconds = seconds - @epoch_gregorian_seconds

  if epoch_seconds < 0 do
    raise ArgumentError, "cannot encode #{naive} as DateTime since it's before Unix epoch"
  end

  <<epoch_seconds::32-little>>
end