Add the broker-comparison module

Kafka, RabbitMQ and Pulsar measured side by side on ordering, replay and
consumer scaling by driving the three client libraries directly, plus an
operational-footprint measurement of each broker's own distribution.

Nine tests, three brokers started without Docker, and every number in the
documentation regenerated by scripts/run-all.sh.

broker-comparison/scripts/pulsar-broker.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# Start a real Apache Pulsar broker with no Docker and no root.
+#
+# The standalone distribution bundles ZooKeeper, BookKeeper and the broker in one process, which
+# is why a single tarball is enough. -nss skips the stream storage (BookKeeper's table service,
+# needed only by stateful Pulsar Functions) and -nfw skips the functions worker; both save
+# several hundred megabytes of heap and a few seconds of startup.
+#
+# PULSAR_HOME must point at an unpacked apache-pulsar-<version>-bin directory. Pulsar 4.2
+# supports Java 17 and 21; the transcripts here were produced on Temurin 21.
+set -eu
+: "${PULSAR_HOME:?set PULSAR_HOME to an unpacked apache-pulsar-*-bin directory}"
+export PULSAR_MEM="${PULSAR_MEM:--Xms384m -Xmx700m -XX:MaxDirectMemorySize=384m}"
+
+cd "$PULSAR_HOME"
+setsid nohup bin/pulsar standalone -nss -nfw > /tmp/pulsar-start.log 2>&1 < /dev/null &
+for _ in $(seq 1 90); do
+  if [ "$(curl -s -o /dev/null -w '%{http_code}' http://127.0.0.1:8080/admin/v2/brokers/version)" = "200" ]; then
+    echo "broker ready on 6650 (admin 8080), version $(curl -s http://127.0.0.1:8080/admin/v2/brokers/version)"
+    exit 0
+  fi
+  sleep 2
+done
+echo "broker did not start; see /tmp/pulsar-start.log" >&2
+exit 1