Remove Rails 5/6 compatibility code

Since we now require Rails 7.0+, removed all EOL version checks:

1. spec/dummy/config/environments/test.rb (lines 19-25)
   Removed: if config.respond_to?(:public_file_server) check and else branch
   Justification: config.public_file_server was introduced in Rails 5.0.
   The old serve_static_files API was deprecated in Rails 5.0 and removed
   in Rails 5.1. Since we require Rails 7.0+, we can safely use
   public_file_server directly.
   Reference: https://guides.rubyonrails.org/5_0_release_notes.html

2. spec/dummy/config/initializers/wrap_parameters.rb (line 11)
   Removed: if respond_to?(:wrap_parameters) check
   Justification: wrap_parameters was introduced in Rails 3.1 (August 2011).
   This check was only needed for Rails 3.0 compatibility. Since we require
   Rails 7.0+, this method is always available.
   Reference: https://api.rubyonrails.org/v7.0/classes/ActionController/ParamsWrapper.html

3. spec/dummy/config/initializers/assets.rb (line 7)
   Removed: if Rails.application.config.respond_to?(:assets) check
   Justification: The assets config has been available since Rails 3.1 with
   the asset pipeline. This check was for Rails 3.0 compatibility. Even in
   Rails 7+ (where asset pipeline is optional), the config still exists.
   Reference: https://guides.rubyonrails.org/asset_pipeline.html

4. lib/vault/encrypted_model.rb (lines 332-340)
   Removed: Version checks for Rails 5.1, 5.2, and 6.0 change tracking APIs
   Justification: Rails 5.1 introduced saved_change_to_attribute?. Rails 5.2
   added previous_changes_include? for deprecation transition. Rails 6.0
   standardized on previous_changes.include?(). The old attribute_changed?
   API was deprecated in Rails 5.1 and removed in Rails 6.0. Since we require
   Rails 7.0+, we can use only previous_changes.include?(attribute).
   Reference: https://api.rubyonrails.org/v7.0/classes/ActiveModel/Dirty.html
   Migration guide: https://github.com/rails/rails/blob/v6.0.0/guides/source/6_0_release_notes.md

Author: chrisarcand

lib/vault/encrypted_model.rb

@@ -329,15 +329,7 @@ def __vault_persist_attribute!(attribute, options)
 
         # Only persist changed attributes to minimize requests - this helps
         # minimize the number of requests to Vault.
-        if ActiveRecord.gem_version >= Gem::Version.new("6.0")
-          return unless previous_changes.include?(attribute)
-        elsif ActiveRecord.gem_version >= Gem::Version.new("5.2")
-          return unless previous_changes_include?(attribute)
-        elsif ActiveRecord.gem_version >= Gem::Version.new("5.1")
-          return unless saved_change_to_attribute?(attribute.to_s)
-        else
-          return unless attribute_changed?(attribute)
-        end
+        return unless previous_changes.include?(attribute)
 
         # Get the current value of the plaintext attribute
         plaintext = attributes[attribute.to_s]

spec/dummy/config/environments/test.rb

@@ -16,13 +16,8 @@
   config.eager_load = false
 
   # Configure static asset server for tests with Cache-Control for performance.
-  if config.respond_to?(:public_file_server)
-    config.public_file_server.enabled = true
-    config.public_file_server.headers = { 'Cache-Control' => 'public, max-age=3600' }
-  else
-    config.serve_static_files   = true
-    config.static_cache_control = 'public, max-age=3600'
-  end
+  config.public_file_server.enabled = true
+  config.public_file_server.headers = { 'Cache-Control' => 'public, max-age=3600' }
 
   # Show full error reports and disable caching.
   config.consider_all_requests_local       = true

spec/dummy/config/initializers/assets.rb

@@ -4,9 +4,7 @@
 # Be sure to restart your server when you modify this file.
 
 # Version of your assets, change this if you want to expire all your assets.
-if Rails.application.config.respond_to?(:assets)
-  Rails.application.config.assets.version = '1.0'
-end
+Rails.application.config.assets.version = '1.0'
 
 # Precompile additional assets.
 # application.js, application.css, and all non-JS/CSS in app/assets folder are already added.

spec/dummy/config/initializers/wrap_parameters.rb

@@ -8,7 +8,7 @@
 
 # Enable parameter wrapping for JSON. You can disable this by setting :format to an empty array.
 ActiveSupport.on_load(:action_controller) do
-  wrap_parameters format: [:json] if respond_to?(:wrap_parameters)
+  wrap_parameters format: [:json]
 end
 
 # To enable root element in JSON for ActiveRecord objects.