[matoous]

API errors currently expose their body only as text. This adds typed Problem details, response headers, and the request URI while keeping the original response text.

try {
    client.checkouts().get("your-checkout-id");
} catch (ApiStatusException error) {
    error.getProblem().ifPresent(problem ->
        System.out.println(problem.type() + ": " + problem.detail()));
}

HTTP failures raise ApiStatusException; connection failures and timeouts raise ApiConnectionException and ApiTimeoutException. All remain catchable as ApiException. Response decoding failures remain distinct from connection failures, and Problem details or titles appear in exception messages. Null-valued Problem extensions are preserved. Malformed error bodies remain HTTP failures with their original text, and asynchronous calls use the same exception types.

The README shows the common error handling path beside SDK usage, with access to the original response for other error details.

Related to sumup/sumup-py#434 and the Python SDK changes in sumup/sumup-py#436.