Add compact-strings module: Compact Strings (JEP 254) measured with JOL on JDK 25, with and without -XX:-CompactStrings, and compact object headers on 25 vs 27

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01KqJyCidz3ZgRyHABv2GVJh

compact-strings/jmh/fetch.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+# Downloads JMH 1.37 and its two runtime dependencies from Maven Central into ./lib, checking each against the published .sha1
+set -euo pipefail
+cd "$(dirname "$0")"; mkdir -p lib
+M=https://repo1.maven.org/maven2
+for a in org/openjdk/jmh/jmh-core/1.37/jmh-core-1.37 \
+         org/openjdk/jmh/jmh-generator-annprocess/1.37/jmh-generator-annprocess-1.37 \
+         net/sf/jopt-simple/jopt-simple/5.0.4/jopt-simple-5.0.4 \
+         org/apache/commons/commons-math3/3.6.1/commons-math3-3.6.1; do
+  f="lib/$(basename "$a").jar"
+  for try in 1 2 3 4 5; do [ -s "$f" ] && break; curl -sfL -o "$f" "$M/$a.jar" || { rm -f "$f"; sleep 5; }; done
+  want=""; for try in 1 2 3 4 5; do want="$(curl -sfL "$M/$a.jar.sha1" | cut -d' ' -f1)" && [ -n "$want" ] && break; sleep 5; done
+  got="$(sha1sum "$f" | cut -d' ' -f1)"
+  [ "$want" = "$got" ] && echo "ok  $f  $got" || { echo "SHA1 MISMATCH $f"; exit 1; }
+done