[Bugfix] Ensure source metadata fetching uses windows-compatible filepaths (#193)

* Fixed underlying bug

* Refactored windows_filenames to be a global flag; added tests

* Added some random test coverage for fun

lib/pinchflat/yt_dlp/media.ex

@@ -63,8 +63,8 @@ defmodule Pinchflat.YtDlp.Media do
         |> response_to_struct()
         |> FunctionUtils.wrap_ok()
 
-      res ->
-        res
+      err ->
+        err
     end
   end