Pin UnlinkPool to internal array accessors

[Th0rgal]

Summary

• bump the benchmark Verity pin to lfglabs-dev/verity@9ebe376 from PR #1868
• update the UnlinkPool case metadata to record the same Verity version
• leave UnlinkPool scoped; this only picks up internal array return registers and memory-backed array accessors

Verification

• lake update verity
• lake build Benchmark.Cases.UnlinkXyz.Pool.Compile
• git diff --check

Note: the compile target still emits the existing unused variable warning for PERMIT2.