Add recursion guard to prevent infinite splitting in batch processing

[Copilot]

The recursive batch splitting logic lacked a termination condition when batch size reaches 1, risking infinite recursion if a single event triggers BatchTooLargeException.

Changes

• cassandra2/PersistentActorUpdateEventProcessor: Added size check in executeBatchV1, executeBatchV1Optimized, and executeBatchV2AndUp
• cassandra4/PersistentActorUpdateEventProcessor: Added size check in executeBatchV3AndUp

When events.size() <= 1 and BatchTooLargeException is caught, throw IllegalStateException with clear diagnostic instead of attempting further splits:

catch(BatchTooLargeException e) {
    if(events.size() <= 1) {
        logger.error("Single event of byteSize {} is too large to execute", e.getBatchSize());
        throw new IllegalStateException("Single event is too large to process", e);
    }
    int half = events.size() / 2;
    // split and recurse...
}

This prevents stack overflow while providing actionable error messages when individual events exceed Cassandra size limits.

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• testng.org
  • Triggering command: /opt/hostedtoolcache/CodeQL/2.23.8/x64/codeql/tools/linux64/java/bin/java /opt/hostedtoolcache/CodeQL/2.23.8/x64/codeql/tools/linux64/java/bin/java -jar /opt/hostedtoolcache/CodeQL/2.23.8/x64/codeql/xml/tools/xml-extractor.jar --fileList=/home/REDACTED/work/elasticactors/.codeql-scratch/dbs/java/working/files-to-index5721431052133658087.list --sourceArchiveDir=/home/REDACTED/work/elasticactors/.codeql-scratch/dbs/java/src --outputDir=/home/REDACTED/work/elasticactors/.codeql-scratch/dbs/java/trap/java (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)