Fixes
- Read Retry-After as whole seconds or an HTTP date, nothing else ([`65e7850`](https://github.com/vpndetection-io/sdk-python/commit/65e785016e8196388be4ec49d9a40b2293a6f928))
- Trim the key and the base URL, and refuse a key no header can carry ([`3dd5e91`](https://github.com/vpndetection-io/sdk-python/commit/3dd5e917740454491b943e0b245c69f7a3da7717))
- Classify a 4xx by status, and fail an unreadable 2xx with its status ([`04f9f06`](https://github.com/vpndetection-io/sdk-python/commit/04f9f067361ee5e8a1ce61b9f4b8842740eb67e3))