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/rabbit-broker.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+# Start a real RabbitMQ broker with no Docker and no root.
+#
+# RabbitMQ is an Erlang application, so an Erlang runtime and epmd on the path are the whole
+# dependency. Point ERL_ROOT at an Erlang installation and RABBITMQ_HOME at an unpacked
+# rabbitmq-server-generic-unix tarball. Ubuntu 22.04 ships Erlang 24, whose newest compatible
+# broker is 3.10.25; 3.11 and later need Erlang 25.
+#
+# The one non-obvious step is starting epmd yourself: rabbitmq-server's own attempt to start it
+# fails in a container without a resolvable hostname, and the failure surfaces as a forty-line
+# Erlang crash dump ending in {'EXIT',nodistribution}.
+set -eu
+: "${ERL_ROOT:?set ERL_ROOT to an Erlang installation directory}"
+: "${RABBITMQ_HOME:?set RABBITMQ_HOME to an unpacked rabbitmq-server-generic-unix directory}"
+
+export PATH="$ERL_ROOT/bin:$ERL_ROOT/erts-"*/bin":$PATH"
+export RABBITMQ_MNESIA_BASE="${RABBITMQ_MNESIA_BASE:-/tmp/rmq/data}"
+export RABBITMQ_LOG_BASE="${RABBITMQ_LOG_BASE:-/tmp/rmq/log}"
+export RABBITMQ_NODENAME="${RABBITMQ_NODENAME:-rabbit@localhost}"
+export HOME="${HOME:-/tmp/rmq}"
+mkdir -p "$RABBITMQ_MNESIA_BASE" "$RABBITMQ_LOG_BASE"
+
+epmd -daemon 2>/dev/null || true
+sleep 1
+setsid nohup "$RABBITMQ_HOME/sbin/rabbitmq-server" > /tmp/rmq/boot.log 2>&1 < /dev/null &
+for _ in $(seq 1 60); do
+  if (echo > /dev/tcp/127.0.0.1/5672) 2>/dev/null; then echo "broker ready on 5672"; exit 0; fi
+  sleep 1
+done
+echo "broker did not start; see /tmp/rmq/boot.log" >&2
+exit 1