Make a deep copy of the _default_attributes in column_defaults

When column_defaults is called it calls `value` on each instance of
Attribute inside the _default_attributes set. Since value is memoized in
the Attribute instance and that Attribute instance is shared across all
instances of a model the next call to the default value will be memozied
not running the proc defined by the user.

Fixes #33031.

activerecord/lib/active_record/model_schema.rb

@@ -375,7 +375,7 @@ module ActiveRecord
       # default values when instantiating the Active Record object for this table.
       def column_defaults
         load_schema
-        @column_defaults ||= _default_attributes.to_hash
+        @column_defaults ||= _default_attributes.deep_dup.to_hash
       end
 
       def _default_attributes # :nodoc:

activerecord/test/cases/attributes_test.rb

@@ -148,6 +148,20 @@ module ActiveRecord
       assert_equal 2, klass.new.counter
     end
 
+    test "procs for default values are evaluated even after column_defaults is called" do
+      klass = Class.new(OverloadedType) do
+        @@counter = 0
+        attribute :counter, :integer, default: -> { @@counter += 1 }
+      end
+
+      assert_equal 1, klass.new.counter
+
+      # column_defaults will increment the counter since the proc is called
+      klass.column_defaults
+
+      assert_equal 3, klass.new.counter
+    end
+
     test "procs are memoized before type casting" do
       klass = Class.new(OverloadedType) do
         @@counter = 0