feat: add statusCode, code, and description to RazorpayException

[sahilleth]

Summary

Adds statusCode, code, and description to RazorpayException to support programmatic error handling.

Problem

RazorpayException only exposes getMessage(), so callers must parse strings to handle different API errors (e.g. 400 vs 404 vs 429). This makes retries, rate limiting, and branching by error type difficult.

Solution

• Add getStatusCode(), getCode(), getDescription() to RazorpayException
• Populate these from API error responses in ApiClient.throwException()
• Use optString for optional code and description (handles OAuth responses where these may be absent)
• Add serialVersionUID for serialization compatibility
• Backward compatible: existing constructors and usage remain unchanged

Usage

try {
Payment payment = razorpayClient.payments.fetch(paymentId);
} catch (RazorpayException e) {
if (Integer.valueOf(429).equals(e.getStatusCode())) {
// Retry with backoff
} else if ("BAD_REQUEST_ERROR".equals(e.getCode())) {
// Handle validation error
}
}

Testing
RazorpayExceptionTest: constructors and getters
PaymentClientTest#fetchThrowsExceptionWithStatusCodeAndErrorCode: API error path