locks: synchronized vs ReentrantLock vs StampedLock companion code

JMH throughput sweep (1-64 threads), 9:1 read-heavy @Group benchmark,
tryLock(timeout) deadlock-avoidance demo, and a JDK21-vs-JDK25 JEP 491
virtual-thread-pinning comparison. Also promotes LICENSE to repo root
now that a second module exists.

locks/scripts/run.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+# Quick ad hoc JMH run against one benchmark class, printed to the terminal. Example:
+#   ./scripts/run.sh IncrementBenchmark -t 8
+#   ./scripts/run.sh ReadHeavyBenchmark
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+BENCH="${1:?Usage: run.sh <BenchmarkClassName> [extra jmh args]}"
+shift || true
+
+JAR=target/benchmarks.jar
+[ -f "$JAR" ] || { echo "Run 'mvn package' first."; exit 1; }
+
+java -jar "$JAR" "$BENCH" "$@"