[Java] Verify direct codecs with GraalVM native-image

[nth-bailey]

Context

Issue #46 and PR #52 delivered Java POJOs, builders, direct StAX codecs, and a JVM JMH comparison. The original issue also proposed GraalVM native-image compilation and startup/size measurements. Those were not run: benchmarks/java/README.md explicitly says its warmed JMH results do not measure native-image startup, executable size, or RSS. It also notes that StAX provider selection and application dependencies may require native-image configuration.

Scope

• Generate a small standalone Java application using --style pojo --feature direct-codec and the standard JDK StAX provider. Compile it with GraalVM native-image and execute XML read/write round trips.
• Record whether the generated model and codec need reflection/resource configuration. If configuration is required, identify whether it comes from PolyXML output, the StAX provider, or other application dependencies.
• Measure native executable size, startup latency, and RSS against the same application's JVM build. Record GraalVM/JDK version, OS, commands, payload, and measurement method. Do not assume the startup or memory targets proposed in [Codegen: Java & C#] Support traditional mutable classes/POJOs with getters, setters, and builders (--style pojo / --builder) #46.
• Document the supported configuration and results in the Java guide or benchmark README. Add an automated smoke test only if a suitable native-image CI runner is available.

This is a verification task, not a requirement to change the existing JVM benchmark or promise universal zero-configuration native-image support.

[nth-bailey]

Closing as not planned. Native-image verification is not a priority for PolyXML right now; the current Java guide already avoids claiming measured GraalVM startup, size, or RSS results.