Harden OpenAI api layer

- Support rate limiting
- Add proper error handling (don't rely on exceptions)

Closes #147

config/config.exs

@@ -72,7 +72,9 @@ config :music_library, BraveSearch,
   user_agent: user_agent,
   api_cooldown: 1000
 
-config :music_library, OpenAI, api_key: "change me"
+config :music_library, OpenAI,
+  api_key: "change me",
+  api_cooldown: 250
 
 # Configure esbuild (the version is required)
 config :esbuild,

config/test.exs

@@ -96,7 +96,8 @@ config :music_library, OpenAI,
   req_options: [
     plug: {Req.Test, OpenAI.API},
     max_retries: 0
-  ]
+  ],
+  api_cooldown: 0
 
 config :phoenix_test, :endpoint, MusicLibraryWeb.Endpoint