Per-vhost message_stats over-counts published messages (sums per-queue counters)

[jage]

Describe the bug

/api/vhosts/:name builds message_stats by summing each queue's counters
(vhost.message_details, vhost.cr:277), so a publish routed to N queues counts as N. The vhost's
own atomic counter holds the true client-publish count and is exposed by /api/overview and
detailed_vhost_messages_published_total, so the surfaces disagree.

Describe your setup

Current main, bin/lavinmq --build-info: 2.8.0-85-g279028c4, default config.

How to reproduce

curl -u guest:guest -XPUT localhost:15672/api/vhosts/t
curl -u guest:guest -H 'content-type: application/json' -XPUT -d '{"type":"fanout","durable":true}' localhost:15672/api/exchanges/t/fx
for q in q1 q2 q3; do
  curl -u guest:guest -H 'content-type: application/json' -XPUT -d '{"durable":true}' localhost:15672/api/queues/t/$q
  curl -u guest:guest -H 'content-type: application/json' -XPOST -d '{"routing_key":""}' localhost:15672/api/bindings/t/e/fx/q/$q
done
curl -u guest:guest -H 'content-type: application/json' -XPOST -d '{"routing_key":"","payload":"x","payload_encoding":"string","properties":{}}' localhost:15672/api/exchanges/t/fx/publish
curl -u guest:guest localhost:15672/api/vhosts/t                  # message_stats.publish = 3
curl -u guest:guest -H 'x-vhost: t' localhost:15672/api/overview  # message_stats.publish = 1

Expected behavior

One client publish counts as one publish, and /api/vhosts/:name agrees with /api/overview.
(Fix: source message_stats from the vhost atomics.)