Define the singleton method directly and drop the call loop

Review feedback: define obj.single with def obj.single instead of
singleton_class.class_exec, and rely on mspec -R rather than an
in-spec loop to exercise JIT-compiled paths.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: Jesse Cai

core/module/ruby2_keywords_spec.rb

@@ -134,23 +134,17 @@ def proc_call(*args)
 
   it "does not copy or unmark the Hash when it is passed directly as a positional argument" do
     obj = Object.new
-    obj.singleton_class.class_exec do
-      def single(arg)
-        arg
-      end
+    def obj.single(arg)
+      arg
     end
 
     h = { a: 1 }
     marked = mark(**h).last
     Hash.ruby2_keywords_hash?(marked).should == true
 
-    # Call repeatedly so implementations that compile methods lazily also
-    # exercise their compiled path (regression: jruby/jruby#9517)
-    100.times do
-      after_usage = obj.single(marked)
-      after_usage.should.equal?(marked)
-      Hash.ruby2_keywords_hash?(after_usage).should == true
-    end
+    after_usage = obj.single(marked)
+    after_usage.should.equal?(marked)
+    Hash.ruby2_keywords_hash?(after_usage).should == true
   end
 
   it "applies to the underlying method and applies across aliasing" do