[FIX] website_sale_aplicoop: three defects in the group order slug

- create(): slugs were only checked against the database, so records created
  in the same batch (duplicating several orders from the list view, importing
  rows sharing a name) collided on group_order_slug_uniq. _generate_unique_slug
  now also skips the slugs already handed out in the batch.
- _redirect_to_slug_url(): `post` is passed as a dict instead of splatted, so a
  query parameter named `suffix` no longer binds to the keyword argument of the
  same name (HTTP 500 on /eskaera/<id>/checkout?suffix=x, and a corrupted path
  on the shop route).
- post-migrate: the backfill runs with tracking_disable, `slug` is tracked and
  the upgrade posted a chatter message on every pre-existing order.

Tests for the two reachable cases: batch create and query parameters kept
across the legacy redirect.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

website_sale_aplicoop/migrations/18.0.1.13.0/post-migrate.py

@@ -17,9 +17,13 @@ def migrate(cr, version):
     if not version:
         return
 
-    env = api.Environment(cr, SUPERUSER_ID, {})
+    # tracking_disable: `slug` is a tracked field, backfilling it would post a
+    # chatter message and notify the followers of every pre-existing order.
+    env = api.Environment(cr, SUPERUSER_ID, {"tracking_disable": True})
     orders = env["group.order"].search([("slug", "=", False)], order="id")
     for order in orders:
+        # One write at a time: the search inside `_generate_unique_slug` flushes
+        # the previous one, so two orders sharing a name get distinct slugs.
         order.slug = order._generate_unique_slug(order.name)
 
     if orders: