Fix RAVV thread-local supplier leaks

[Trihedron1240]

Summary

• Fixes RandomAccessVectorValues thread-local supplier cleanup by exposing a closeable supplier path.
• Closes thread-local copies owned by ExplicitThreadLocal, including copies created during graph build and quantization flows.
• Adds regression tests proving shared RAVV copies are closed and GraphIndexBuilder releases copied vector values.

Closes #635

Root Cause

RandomAccessVectorValues.threadLocalSupplier() used ExplicitThreadLocal internally but returned only tl::get, so callers had no way to close the thread-local container or the copied vector values it owned. This leaked closeable copies created for shared RAVV implementations.

Validation

• Before fix: focused regression failed; graph build created 12 RAVV copies and closed 0.
• After fix: focused regression passed; all created RAVV copies were closed.
• git diff --check origin/main...HEAD
• mvn -B verify using local JDK 25
• mvn -B -Pjdk20 -am -pl jvector-tests test using local JDK 25
• mvn -B -Pjdk11 -am -pl jvector-tests test using local JDK 25

Notes

The GitHub Actions AVX/native lanes and manual benchmark workflow should still be reviewed on GitHub runner hardware.