Normalizing feed page size (#15326)

This commit removes a handful of magic numbers and instead relies on a
constant.

This has a small impact in that the Basic feed will now return 50
articles instead of 25.  However, normalizing the feed pagination window
size helps reduce some oddities in reporting.

In addition, this might be something we consider giving administrators
the ability to set (with default options, because we shouldn't allow
page sizes of 10_000 as that's a massive memory hog).

Related to #14709

app/models/article.rb

@@ -9,6 +9,8 @@ class Article < ApplicationRecord
   acts_as_taggable_on :tags
   resourcify
 
+  DEFAULT_FEED_PAGINATION_WINDOW_SIZE = 50
+
   attr_accessor :publish_under_org
   attr_writer :series
 

app/services/articles/feeds/basic.rb

@@ -1,7 +1,7 @@
 module Articles
   module Feeds
     class Basic
-      def initialize(user: nil, number_of_articles: 25, page: 1, tag: nil)
+      def initialize(user: nil, number_of_articles: Article::DEFAULT_FEED_PAGINATION_WINDOW_SIZE, page: 1, tag: nil)
         @user = user
         @number_of_articles = number_of_articles
         @page = page

app/services/articles/feeds/large_forem_experimental.rb

@@ -1,7 +1,7 @@
 module Articles
   module Feeds
     class LargeForemExperimental
-      def initialize(user: nil, number_of_articles: 50, page: 1, tag: nil)
+      def initialize(user: nil, number_of_articles: Article::DEFAULT_FEED_PAGINATION_WINDOW_SIZE, page: 1, tag: nil)
         @user = user
         @number_of_articles = number_of_articles
         @page = page

app/services/articles/feeds/latest.rb

@@ -3,7 +3,7 @@ module Articles
     module Latest
       MINIMUM_SCORE = -20
 
-      def self.call(tag: nil, number_of_articles: 50, page: 1)
+      def self.call(tag: nil, number_of_articles: Article::DEFAULT_FEED_PAGINATION_WINDOW_SIZE, page: 1)
         Articles::Feeds::Tag.call(tag)
           .order(published_at: :desc)
           .where("score > ?", MINIMUM_SCORE)

app/services/articles/feeds/tag.rb

@@ -1,7 +1,7 @@
 module Articles
   module Feeds
     module Tag
-      def self.call(tag = nil, number_of_articles: 50, page: 1)
+      def self.call(tag = nil, number_of_articles: Article::DEFAULT_FEED_PAGINATION_WINDOW_SIZE, page: 1)
         articles =
           if tag.present?
             if FeatureFlag.enabled?(:optimize_article_tag_query)

app/services/articles/feeds/timeframe.rb

@@ -1,7 +1,7 @@
 module Articles
   module Feeds
     module Timeframe
-      def self.call(timeframe, tag: nil, number_of_articles: 50, page: 1)
+      def self.call(timeframe, tag: nil, number_of_articles: Article::DEFAULT_FEED_PAGINATION_WINDOW_SIZE, page: 1)
         articles = ::Articles::Feeds::Tag.call(tag)
 
         articles