Initial yt-dlp implementation (#3)

* Added basic runner for yt-dlp commands

* Updated formatting rules

* Added JSON runner; Added test script for CLI interactions

* Reworked yt-dlp runner; added proper test mocks

mix.exs

@@ -50,7 +50,8 @@ defmodule Pinchflat.MixProject do
       {:gettext, "~> 0.20"},
       {:jason, "~> 1.2"},
       {:dns_cluster, "~> 0.1.1"},
-      {:plug_cowboy, "~> 2.5"}
+      {:plug_cowboy, "~> 2.5"},
+      {:mox, "~> 1.0", only: :test}
     ]
   end