Store ranges as tuples in Sequence :queue

Found a memory savings for `Indexer.Sequence`: store Ranges as tuples in
the `:queue` as the tuples take up less space than than the `%Range{}`
struct, but only after garbage-collection.  The incoming and outgoing
format is still Ranges, so this is a non-breaking implementation detail
only.

```elixir
  test "memory usage" do
    {:ok, pid} = Sequence.start_link(ranges: [max_block_number..0],
step: -10)

    Process.info(pid, :memory) |> IO.inspect(label: "BEFORE GC")

    :erlang.garbage_collect(pid)

    Process.info(pid, :memory) |> IO.inspect(label: "AFTER GC")
  end
```

| max_block_number | Garbage Collection | Ranges (bytes) | Tuples (bytes) | Tuples / Ranges (%) |
|------------------|--------------------|----------------|----------------|---------------------|
| 5,000,000        | Before             | 41,050,964     | 22,445,660     | 54.68               |
| 5,000,000        | After              | 34,386,756     | 23,879,996     | 69.45               |
| 10,000,000       | Before             | 80,889,772     | 47,928,116     | 59.24               |
| 10,000,000       | After              | 71,303,316     | 49,516,492     | 69.44               |

apps/indexer/lib/indexer/sequence.ex

@@ -182,8 +182,8 @@ defmodule Indexer.Sequence do
   def handle_call(:pop, _from, %__MODULE__{queue: queue, current: current, step: step} = state) do
     {reply, new_state} =
       case {current, :queue.out(queue)} do
-        {_, {{:value, range}, new_queue}} ->
+        {_, {{:value, {first, last}}, new_queue}} ->
-          {range, %__MODULE__{state | queue: new_queue}}
+          {first..last, %__MODULE__{state | queue: new_queue}}
 
         {nil, {:empty, new_queue}} ->
           {:halt, %__MODULE__{state | queue: new_queue}}
@@ -251,8 +251,8 @@ defmodule Indexer.Sequence do
     {:error, "Range (#{inspect(range)}) direction is opposite step (#{step}) direction"}
   end
 
-  defp reduce_chunked_range(_.._ = range, count, step, initial, reducer) when count <= abs(step) do
+  defp reduce_chunked_range(first..last, count, step, initial, reducer) when count <= abs(step) do
-    {:ok, reducer.(range, initial)}
+    {:ok, reducer.({first, last}, initial)}
   end
 
   defp reduce_chunked_range(first..last, _, step, initial, reducer) do
@@ -277,7 +277,7 @@ defmodule Indexer.Sequence do
             {:cont, full_chunk_last}
           end
 
-        {action, reducer.(chunk_first..chunk_last, acc)}
+        {action, reducer.({chunk_first, chunk_last}, acc)}
       end)
 
     {:ok, final}