Refactor and add tests for OpenAI namespace

lib/open_ai.ex

@@ -2,7 +2,7 @@ defmodule OpenAI do
   alias OpenAI.API
 
   def gpt(completion) do
-    API.gpt(completion, api_key())
+    API.gpt(completion, config())
   end
 
   def chat_stream(messages, opts \\ []) when is_list(messages) do
@@ -11,18 +11,15 @@ defmodule OpenAI do
     instructions = Keyword.get(opts, :instructions, "")
     on_chunk = Keyword.fetch!(opts, :on_chunk)
 
-    case API.chat_stream(messages, instructions, model, temperature, api_key(), on_chunk) do
+    case API.chat_stream(messages, instructions, model, temperature, config(), on_chunk) do
       :ok -> :ok
       {:error, _reason} = error -> error
     end
   end
 
   def embeddings(text) do
-    API.get_embeddings(text, api_key())
+    API.get_embeddings(text, config())
   end
 
-  defp api_key do
-    Application.get_env(:music_library, __MODULE__)
-    |> Keyword.fetch!(:api_key)
-  end
+  defp config, do: OpenAI.Config.resolve(:music_library)
 end