make Ch.stream emit Ch.Result.t

[ruslandoga]

This PR makes Ch.stream emit Ch.Result.t structs. This makes it possible to Stream.into or Enum.into it into files and stuff (Collectable implementations).

Example from plausible/analytics#3692

  @doc """
  Creates a streamable Zip archive from the provided (named) Ecto queries.

  Example usage:

      {:ok, pool} = Ch.start_link(pool_size: 1)

      DBConnection.run(pool, fn conn ->
        conn
        |> stream_archive(export_queries(_site_id = 1), format: "CSVWithNames")
        |> Stream.into(File.stream!("export.zip"))
        |> Stream.run()
      end)

  """
  @spec stream_archive(DBConnection.conn(), %{String.t() => Ecto.Query.t()}, [Ch.query_option()]) ::
          Enumerable.t()
  def stream_archive(conn, named_queries, opts \\ []) do
    entries =
      Enum.map(named_queries, fn {name, query} ->
        {sql, params} = Plausible.ClickhouseRepo.to_sql(:all, query)

        datastream =
          conn
          |> Ch.stream(sql, params, opts)
          |> Stream.map(fn %Ch.Result{data: data} -> data end)

        Zstream.entry(name, datastream, coder: Zstream.Coder.Stored)
      end)

    Zstream.zip(entries)
  end