Remove dependency on observer

Gemfile.lock

@@ -3,7 +3,6 @@ PATH
   specs:
     factory_bot (6.4.3)
       activesupport (>= 5.0.0)
-      observer
 
 GEM
   remote: https://rubygems.org/
@@ -74,7 +73,6 @@ GEM
     middleware (0.1.0)
     minitest (5.14.3)
     multi_test (0.1.2)
-    observer (0.1.2)
     parallel (1.22.1)
     parser (3.1.2.1)
       ast (~> 2.4.1)

factory_bot.gemspec

@@ -27,7 +27,6 @@ Gem::Specification.new do |s|
   }
 
   s.add_dependency("activesupport", ">= 5.0.0")
-  s.add_dependency("observer") if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new("3.3")
 
   s.add_development_dependency("activerecord")
   s.add_development_dependency("appraisal")

lib/factory_bot/evaluation.rb

@@ -1,13 +1,10 @@
-require "observer"
-
 module FactoryBot
   class Evaluation
-    include Observable
-
-    def initialize(evaluator, attribute_assigner, to_create)
+    def initialize(evaluator, attribute_assigner, to_create, observer)
       @evaluator = evaluator
       @attribute_assigner = attribute_assigner
       @to_create = to_create
+      @observer = observer
     end
 
     delegate :object, :hash, to: :@attribute_assigner
@@ -20,8 +17,7 @@ def create(result_instance)
     end
 
     def notify(name, result_instance)
-      changed
-      notify_observers(name, result_instance)
+      @observer.update(name, result_instance)
     end
   end
 end

lib/factory_bot/factory.rb

@@ -36,9 +36,9 @@ def run(build_strategy, overrides, &block)
       evaluator = evaluator_class.new(strategy, overrides.symbolize_keys)
       attribute_assigner = AttributeAssigner.new(evaluator, build_class, &compiled_constructor)
 
+      observer = CallbacksObserver.new(callbacks, evaluator)
       evaluation =
-        Evaluation.new(evaluator, attribute_assigner, compiled_to_create)
-      evaluation.add_observer(CallbacksObserver.new(callbacks, evaluator))
+        Evaluation.new(evaluator, attribute_assigner, compiled_to_create, observer)
 
       strategy.result(evaluation).tap(&block)
     end

spec/factory_bot/factory_spec.rb

@@ -294,7 +294,7 @@ def build_factory
     attribute = FactoryBot::Attribute::Dynamic.new(:name, false, -> { "value" })
     attributes = [attribute]
     declaration = FactoryBot::Declaration::Dynamic.new(:name, false, -> { "value" })
-    strategy = double("strategy", result: "result", add_observer: true)
+    strategy = double("strategy", result: "result")
     define_model("User", name: :string)
     allow(FactoryBot::Declaration::Dynamic).to receive(:new)
       .and_return declaration