Improve attribute methods generation

I'm currently working through Ruby warnings in our app, and one of the
top source is from ActiveModel Serializer sub classes.

Usually they look like:

```
class SomethingSerializer < AMS
  attributes :title, :body

  def title # method redefinition warning
    titleize
  end
end
```

One solution would be to call `attributes` at the end of the method,
so that `attributes` skips defining these, but it's quite unatural.

Instead we can use the self alias trick to mark these generated
methods as OK to redefine. An alternative would be to define them
in an included module like Active Model does, but not sure if it's
worth it.

While I was at it, I improved the way these methods are generated.

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ### [0-9-stable](https://github.com/rails-api/active_model_serializers/compare/v0.9.12...0-9-stable)
 
+- Perf
+  - [#2471](https://github.com/rails-api/active_model_serializers/pull/2471) Generate better attribute accessors, that also don't trigger warnings when redefined. (@byroot)
+
 ### [v0.9.12 (2024-04-11)](https://github.com/rails-api/active_model_serializers/compare/v0.9.11...v0.9.12)
 
 - Fix

Gemfile

@@ -72,8 +72,10 @@ group :test do
   platforms(*(@windows_platforms + [:ruby])) do
     if RUBY_VERSION < '2.5' || version < '6'
       gem 'sqlite3', '~> 1.3.13'
+    elsif version >= '8'
+      gem 'sqlite3', '>= 2'
     else
-      gem 'sqlite3'
+      gem 'sqlite3', '< 2'
     end
   end
   platforms :jruby do

lib/active_model/serializer.rb

@@ -90,15 +90,27 @@ def root_name
       end
 
       def attributes(*attrs)
+        # Use `class_eval` rather than `define_method` for faster access
+        # and avoid retaining objects in the closure.
+        # Batch all methods in a single `class_eval` for efficiceny,
+        # and define all methods on the same line so the eventual backtrace
+        # properly maps to the `attributes` call.
+        source = ["# frozen_string_literal: true\n"]
         attrs.each do |attr|
           striped_attr = strip_attribute attr
 
           @_attributes << striped_attr
 
-          define_method striped_attr do
-            object.read_attribute_for_serialization attr
-          end unless method_defined?(attr)
+          unless method_defined?(attr)
+            source <<
+            "def #{striped_attr}" <<
+              "object.read_attribute_for_serialization(#{attr.inspect})" <<
+            "end" <<
+            "alias_method :#{striped_attr}, :#{striped_attr}" # suppress method redefinition warning
+          end
         end
+        caller = caller_locations(1, 1).first
+        class_eval(source.join(";"), caller.path, caller.lineno - 1)
       end
 
       def has_one(*attrs)