[FIX] website_forum: use read_group to compute user statistics

Instead of doing 1 search_count / user in the loop, use read_group to fetch
data in batch.

Also remove an unnecessary import.

Task-3240082 (Forum: Reorganize and lint module)

Part-of: odoo/odoo#114841

addons/website_forum/models/res_users.py

@@ -1,20 +1,31 @@
 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
-from odoo import api, fields, models
+from odoo import fields, models
 
 
 class Users(models.Model):
     _inherit = 'res.users'
 
     create_date = fields.Datetime('Create Date', readonly=True, index=True)
-    forum_waiting_posts_count = fields.Integer('Waiting post', compute="_get_user_waiting_post")
+    forum_waiting_posts_count = fields.Integer(
+        'Waiting post', compute="_compute_forum_waiting_posts_count")
 
-    def _get_user_waiting_post(self):
+    def _compute_forum_waiting_posts_count(self):
+        if not self.ids:
+            self.forum_waiting_posts_count = 0
+            return
+        read_group_res = self.env['forum.post']._read_group(
+            [('create_uid', 'in', self.ids), ('state', '=', 'pending'), ('parent_id', '=', False)],
+            ['create_uid'],
+            ['create_uid'],
+        )
+        mapping = {
+            res_group['create_uid'][0]: res_group['create_uid_count']
+            for res_group in read_group_res
+        }
         for user in self:
-            Post = self.env['forum.post']
-            domain = [('parent_id', '=', False), ('state', '=', 'pending'), ('create_uid', '=', user.id)]
-            user.forum_waiting_posts_count = Post.search_count(domain)
+            user.forum_waiting_posts_count = mapping.get(user.id, 0)
 
     # Wrapper for call_kw with inherits
     def open_website_url(self):