feat(network): max_attempts config, NatsConnection readiness probe, correlation_id field

[mvillmow]

Summary

• Add max_attempts config option to NatsListener for non-daemon callers #331: Added max_attempts field (default: 3) to NATSListenerConfig; NATSListener::start() now retries js_Subscribe up to max_attempts times, logging each failed attempt, before returning the final error status.
• Wire NatsConnection into HealthCheckServer readiness probe #204: Added NatsConnectionCheck callback type and setNatsConnectionCheck() method to HealthCheckServer; the /ready readiness probe now returns 503 until this callback (e.g. [&conn]{ return conn.isConnected(); }) returns true, before evaluating the custom ReadinessCheck.
• Include correlation_id field in KeystoneMessage for cross-host tracing #285: Added std::optional<std::string> correlation_id to KeystoneMessage for cross-host distributed tracing; propagated through SerializableMessage (correlation_id + has_correlation_id fields) in both fromKeystoneMessage() and toKeystoneMessage().

Test plan

• Build debug preset: cmake --preset debug && cmake --build --preset debug
• Run unit tests: ctest --preset debug --output-on-failure
• Verify NATSListenerConfig{.max_attempts=1} disables retries; max_attempts=3 retries up to 3 times
• Verify HealthCheckServer constructed with nats_connection_check=[]{return false;} returns 503 on /ready
• Verify KeystoneMessage round-trips correlation_id through MessageSerializer::serialize/deserialize
• Format check: just format-check

Closes #331
Closes #204
Closes #285

🤖 Generated with Claude Code

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