Improve Lightlist performance

[8Keep]

Stacked on #2778; the first commit is the JMH harness.

Summary

• avoid copying and clearing unused retained LightList backing capacity
• use bulk copy paths where LightList.update() has no filter
• keep the retained sort buffer sized to active lights rather than backing-array capacity
• remove unused distToOwner state
• add focused tests for removal ordering, update ordering/filtering, and sorting after retained capacity

Benchmarking

The harness includes mutation and retained-capacity sort benchmarks. The original unfiltered updateFromLocalAndParent number is not presented as a production claim: Spatial.updateWorldLightList() uses a global-light filter. updateWithGlobalLightFilter covers that representative path; compact local measurements were promising at medium/large list sizes but need longer controlled runs before a PR performance claim.

Testing

./gradlew :jme3-core:test --tests com.jme3.light.LightListTest --tests com.jme3.light.LightSortTest :jme3-benchmark:jmh -PjmhArgs='-l'

[gemini-code-assist]

Code Review

This pull request introduces the Java Microbenchmark Harness (JMH) to the project, adding a dedicated benchmark source set and several performance tests for bounding volumes, light lists, and geometry lists. In LightList, several methods including remove, clear, sort, and update were optimized using System.arraycopy and Arrays.fill to improve efficiency. Feedback suggests removing the distToOwner array and its associated logic in LightList, as it is currently dead code and not correctly synchronized during element removal.

[riccardobl]

Benchmarks should be moved into their own jme3-benchmark module, so that we don't have to deal with them in the normal codebase.

Other than that and the distToOwner comment by gemini, everything looks good.

[8Keep]

Should be solid now

[8Keep]

@riccardobl could you take another look?