Refactor modules into contexts (#78)

* [WIP] break out a few contexts, start refactoring fast index modules

* [WIP] more contexts, this time around slow indexing and downloads

* [WIP] got all tests passing

* [WIP] Added moduledocs

* Built a genserver to rename old jobs on boot

* Added a module naming check; moved things around

* Fixed specs

lib/pinchflat/filesystem/filesystem_data_worker.ex

@@ -0,0 +1,27 @@
+defmodule Pinchflat.Filesystem.FilesystemDataWorker do
+  @moduledoc false
+
+  use Oban.Worker,
+    queue: :media_local_metadata,
+    tags: ["media_item", "media_metadata", "local_metadata"],
+    max_attempts: 1
+
+  alias Pinchflat.Media
+  alias Pinchflat.Filesystem.FilesystemHelpers
+
+  @impl Oban.Worker
+  @doc """
+  For a given media item, compute and save metadata about the file on-disk.
+
+  Returns :ok
+  """
+  def perform(%Oban.Job{args: %{"id" => media_item_id}}) do
+    media_item = Media.get_media_item!(media_item_id)
+
+    FilesystemHelpers.compute_and_save_media_filesize(media_item)
+
+    # Don't retry on failure - if it didn't work immediately there's no
+    # reason to believe it will work later.
+    :ok
+  end
+end