PERF: Improve performance of `most_replied_to_users` (#26373)

This PR improves the performance of the `most_replied_to_users` method on the `UserSummary` model.

### Old Query
```ruby
    post_query
      .joins(
        "JOIN posts replies ON posts.topic_id = replies.topic_id AND posts.reply_to_post_number = replies.post_number",
      )
      # We are removing replies by @user, but we can simplify this by getting the using the user_id on the posts.
      .where("replies.user_id <> ?", @user.id)
      .group("replies.user_id")
      .order("COUNT(*) DESC")
      .limit(MAX_SUMMARY_RESULTS)
      .pluck("replies.user_id, COUNT(*)")
      .each { |r| replied_users[r[0]] = r[1] }
```
 
### Old Query with corrections

```ruby
post_query
  .joins(
    "JOIN posts replies ON posts.topic_id = replies.topic_id AND replies.reply_to_post_number = posts.post_number",
  )
  # Remove replies by @user but instead look on loaded posts (we do this so we don't count self replies)
  .where("replies.user_id <> posts.user_id")
  .group("replies.user_id")
  .order("COUNT(*) DESC")
  .limit(MAX_SUMMARY_RESULTS)
  .pluck("replies.user_id, COUNT(*)")
  .each { |r| replied_users[r[0]] = r[1] }
```

### New Query
```ruby
    post_query
      .joins(
        "JOIN posts replies ON posts.topic_id = replies.topic_id AND posts.reply_to_post_number = replies.post_number",
      )
      # Only include regular posts in our joins, this makes sure we don't have the bloat of loading private messages
      .joins(
        "JOIN topics ON replies.topic_id = topics.id AND topics.archetype <> 'private_message'",
      )
      # Only include visible post types, so exclude posts like whispers, etc
      .joins(
        "AND replies.post_type IN (#{Topic.visible_post_types(@user, include_moderator_actions: false).join(",")})",
      )
      .where("replies.user_id <> posts.user_id")
      .group("replies.user_id")
      .order("COUNT(*) DESC")
      .limit(MAX_SUMMARY_RESULTS)
      .pluck("replies.user_id, COUNT(*)")
      .each { |r| replied_users[r[0]] = r[1] }
```

# Conclusion

`most_replied_to_users` was untested, so I introduced a test for the logic, and have confirmed that it passes on both the new query **AND** the old query. 

Thank you @danielwaterworth for the debugging assistance.

app/models/user_summary.rb

@@ -88,7 +88,13 @@ class UserSummary
       .joins(
         "JOIN posts replies ON posts.topic_id = replies.topic_id AND posts.reply_to_post_number = replies.post_number",
       )
-      .where("replies.user_id <> ?", @user.id)
+      .joins(
+        "JOIN topics ON replies.topic_id = topics.id AND topics.archetype <> 'private_message'",
+      )
+      .joins(
+        "AND replies.post_type IN (#{Topic.visible_post_types(@user, include_moderator_actions: false).join(",")})",
+      )
+      .where("replies.user_id <> posts.user_id")
       .group("replies.user_id")
       .order("COUNT(*) DESC")
       .limit(MAX_SUMMARY_RESULTS)

spec/models/user_summary_spec.rb

@@ -90,4 +90,45 @@ RSpec.describe UserSummary do
     expect(summary.top_categories.first[:topic_count]).to eq(1)
     expect(summary.top_categories.first[:post_count]).to eq(1)
   end
+
+  it "returns the most replied to users" do
+    topic1 = create_post.topic
+    topic1_post = create_post(topic: topic1)
+    topic1_reply =
+      create_post(topic: topic1, reply_to_post_number: topic1_post.post_number, user: topic1.user)
+
+    # Create a second topic by the same user as topic1
+    topic2 = create_post(user: topic1.user).topic
+    topic2_post = create_post(topic: topic2)
+    topic2_reply =
+      create_post(topic: topic2, reply_to_post_number: topic2_post.post_number, user: topic2.user)
+
+    # Don't include replies to whispers
+    topic3 = create_post(user: topic1.user).topic
+    topic3_post = create_post(topic: topic3, post_type: Post.types[:whisper])
+    topic3_reply =
+      create_post(topic: topic3, reply_to_post_number: topic3_post.post_number, user: topic3.user)
+
+    # Don't include replies to private messages
+    replied_to_user = Fabricate(:user)
+    topic4 =
+      create_post(
+        user: topic1.user,
+        archetype: Archetype.private_message,
+        target_usernames: [replied_to_user.username],
+      ).topic
+    topic4_post = create_post(topic: topic4, user: replied_to_user)
+    topic4_reply =
+      create_post(topic: topic4, reply_to_post_number: topic4_post.post_number, user: topic4.user)
+
+    user_summary = UserSummary.new(topic1.user, Guardian.new(topic1.user))
+    most_replied_to_users = user_summary.most_replied_to_users
+
+    counts =
+      most_replied_to_users
+        .index_by { |user_with_count| user_with_count[:id] }
+        .transform_values { |c| c[:count] }
+
+    expect(counts).to eq({ topic1_post.user_id => 1, topic2_post.user_id => 1 })
+  end
 end