Refactor Zeitwerk setup in Action Cable

I am trying to find a sweet spot here.

Personally, not quite satisfied by having lib/action_cable/zeitwerk.rb. At the
same time, trying to avoid too taking much space in lib/action_cable.rb.

This patch also moves

    require_relative "action_cable/version"

within ActionCable. Why? In a project, I like that the entrypoint defines the
namespace. That is the main file for that namespace.

Then, files below have it already created, and reopen it.

I just find this deliberate order of execution to be natural, hierarchical,
matching the project structure.

actioncable/lib/action_cable.rb

@@ -25,11 +25,26 @@
 
 require "active_support"
 require "active_support/rails"
+require "zeitwerk"
 
-require_relative "action_cable/version"
-require_relative "action_cable/zeitwerk"
+Zeitwerk::Loader.for_gem.tap do |loader|
+  loader.ignore(
+    "#{__dir__}/rails", # Contains generators, templates, docs, etc.
+    "#{__dir__}/action_cable/gem_version.rb"
+  )
+
+  loader.do_not_eager_load(
+    "#{__dir__}/action_cable/subscription_adapter", # Adapters are required and loaded on demand.
+    "#{__dir__}/action_cable/test_helper.rb",
+    Dir["#{__dir__}/action_cable/**/test_case.rb"]
+  )
+
+  loader.inflector.inflect("postgresql" => "PostgreSQL")
+end.setup
 
 module ActionCable
+  require_relative "action_cable/version"
+
   INTERNAL = {
     message_types: {
       welcome: "welcome",

actioncable/lib/action_cable/zeitwerk.rb

@@ -1,32 +0,0 @@
-# frozen_string_literal: true
-
-require "zeitwerk"
-
-lib = File.expand_path("..", __dir__)
-
-loader = Zeitwerk::Loader.new
-loader.tag = "action_cable"
-
-loader.push_dir(lib)
-
-loader.ignore(
-  __FILE__,
-  "#{lib}/action_cable/gem_version.rb",
-  "#{lib}/action_cable/version.rb",
-  # lib/rails contains generators, templates, documentation, etc. Generators are
-  # required on demand, so we can just ignore it all.
-  "#{lib}/rails",
-)
-
-loader.do_not_eager_load(
-  # Adapters are required and loaded on demand.
-  "#{lib}/action_cable/subscription_adapter",
-  "#{lib}/action_cable/test_helper.rb",
-  "#{lib}/action_cable/test_case.rb",
-  "#{lib}/action_cable/connection/test_case.rb",
-  "#{lib}/action_cable/channel/test_case.rb"
-)
-
-loader.inflector.inflect("postgresql" => "PostgreSQL")
-
-loader.setup