OAuth app credentials for MyAnimeList.
Public-data calls (MyAnimeList.search/4, MyAnimeList.get/4) only need
a bare client_id string, but the OAuth flow needs the full app
registration:
client = %MyAnimeList.Client{
client_id: System.fetch_env!("MAL_CLIENT_ID"),
client_secret: System.fetch_env!("MAL_CLIENT_SECRET"),
redirect_uri: "https://example.com/auth/mal/callback"
}req_options is merged into every request this client makes — the seam
for Req.Test in your tests, or for custom retry/timeout behaviour.