Stabilize external-DTD dictionary loading in MessageTest with short timeouts and bounded retries

[Copilot]

MessageTest.shouldConvertToXmlWhenDataDictionaryLoadedWithExternalDTD was intermittently failing because parsing FIX_External_DTD.xml can block on w3.org network latency (default ~30s timeout). This updates the test path to fail faster per attempt and retry a small number of times before surfacing an error.

• Problem focus

  • The flaky path is external DTD resolution during DataDictionary construction in the XML conversion test.
  • Failures are transient network-bound, not deterministic parsing failures.

• Change set

  • Added a dedicated helper in quickfix.MessageTest to load FIX_External_DTD.xml with:
    • reduced JVM URL timeouts (sun.net.client.defaultConnectTimeout, sun.net.client.defaultReadTimeout) set to 5000ms
    • bounded retries (3 attempts)
    • short exponential backoff between attempts (250ms, 500ms)
  • Ensured system properties are always restored in finally to avoid timeout leakage into other tests.
  • Preserved root cause on final failure and wrapped with an aggregate message including attempt count.

• Test update usage

  • shouldConvertToXmlWhenDataDictionaryLoadedWithExternalDTD now uses the retrying loader instead of directly instantiating DataDictionary.

for (int attempt = 1; attempt <= EXTERNAL_DTD_LOAD_RETRIES; attempt++) {
    try {
        return new DataDictionary("FIX_External_DTD.xml", DocumentBuilderFactory::newInstance);
    } catch (ConfigError e) {
        lastError = e;
        if (attempt < EXTERNAL_DTD_LOAD_RETRIES) {
            Thread.sleep((1L << (attempt - 1)) * EXTERNAL_DTD_RETRY_DELAY_MILLIS);
        }
    }
}
throw new ConfigError("Failed to load FIX_External_DTD.xml after "
        + EXTERNAL_DTD_LOAD_RETRIES + " attempts", lastError);