Move BackfillScrobbledTracks worker under MusicLibrary namespace

lib/last_fm/worker/backfill_scrobbled_tracks.ex

@@ -1,29 +0,0 @@
-defmodule LastFm.Worker.BackfillScrobbledTracks do
-  use Oban.Worker, queue: :heavy_writes, max_attempts: 3
-
-  alias MusicLibrary.BackgroundRepo
-
-  @backfill_delay 1
-  @batch_size 200
-
-  @impl Oban.Worker
-  def perform(%{args: %{"to_uts" => to_uts}}) do
-    # importing is an all or nothing operation, which means that we can
-    # use the returning count to determine if we reached the end of the backfilling
-    # process.
-    case LastFm.Import.batch(to_uts: to_uts, limit: @batch_size) do
-      {:ok, @batch_size} ->
-        next_to_uts = LastFm.lowest_scrobbled_at_uts()
-
-        %{"to_uts" => next_to_uts}
-        |> new(schedule_in: @backfill_delay)
-        |> BackgroundRepo.insert()
-
-      {:ok, _other_count} ->
-        :ok
-
-      error ->
-        error
-    end
-  end
-end