Reduce Object Header Size and Save Memory in Java 25

Java 25 introduces JEP 519, which makes Compact Object Headers a production feature in HotSpot JVM. This reduces object header size from 96-128 bits to 64 bits on 64-bit platforms by merging the mark word and class pointer. The change delivers 10-20% memory reduction for applications with many small objects, improves cache utilization, and reduces garbage collection pressure. Benchmarks show 22% heap space reduction and 15% fewer GC cycles in SPECjbb2015 tests. The feature requires compressed class pointers and is not yet supported by JVMCI on x64.