[FIX] website: perf - prefetch access token to avoid extra request

Access_token has a restricted group, so it not fetched by defaut.

In our case, we know that after the first access to partner_id, that will fill
the cache without access_token, we will access access_token (so new query).

So we access first the access_token, to have only one request that fill the
cache with the access_token, and the partner_id used later.

Related to #47257
task-2211013

X-original-commit: 7dd69d10d00d5f4a7c12ec414d63f868a10683be

addons/website/models/website_visitor.py

@@ -172,6 +172,9 @@ class WebsiteVisitor(models.Model):
         access_token = request.httprequest.cookies.get('visitor_uuid')
         if access_token:
             visitor = Visitor.with_context(active_test=False).search([('access_token', '=', access_token)])
+            # Prefetch access_token and other fields. Since access_token has a restricted group and we access
+            # a non restricted field (partner_id) first it is not fetched and will require an additional query to be retrieved.
+            visitor.access_token
 
         if not self.env.user._is_public():
             partner_id = self.env.user.partner_id