rails: update framework files and settings to 7.0.

* Update framework files with `bin/rails app:update`.
* Update to use new Rails 7.0 default settings, except for a couple
  things regarding new cookie and cache formats that would prevent us
  from rolling back to Rails 6.1 if necessary.

config/environments/test.rb

@@ -8,17 +8,18 @@ require "active_support/core_ext/integer/time"
 Rails.application.configure do
   # Settings specified here will take precedence over those in config/application.rb.
 
+  # Turn false under Spring and add config.action_view.cache_template_loading = true.
   config.cache_classes = true
 
-  # Do not eager load code on boot. This avoids loading your whole application
-  # just for the purpose of running a single test. If you are using a tool that
-  # preloads Rails for running tests, you may have to set it to true.
-  config.eager_load = false
+  # Eager loading loads your whole application. When running a single test locally,
+  # this probably isn't necessary. It's a good idea to do in a continuous integration
+  # system, or in some way before deploying your code.
+  config.eager_load = ENV["CI"].present?
 
   # Configure public file server for tests with Cache-Control for performance.
   config.public_file_server.enabled = true
   config.public_file_server.headers = {
-    'Cache-Control' => "public, max-age=#{1.hour.to_i}"
+    "Cache-Control" => "public, max-age=#{1.hour.to_i}"
   }
 
   # Show full error reports and disable caching.