Fix LoadError and warnings for fiddle

Author: k0kubun

harness/harness-common.rb

@@ -70,11 +70,17 @@ def is_macos
 end
 
 def get_maxrss
-  unless $LOAD_PATH.resolve_feature_path("fiddle")
-    gem "fiddle", ">= 1.1.8" # For ruby 3.5.0-dev compatibility
+  # In Ruby 3.5+, fiddle is no longer a default gem. Load the bundled-gem fiddle instead.
+  unless $LOAD_PATH.resolve_feature_path('fiddle') # Ruby 3.5+
+    bundler_ui_level, Bundler.ui.level = Bundler.ui.level, :error if defined?(Bundler) # suppress warnings from force_activate
+    Gem::BUNDLED_GEMS.force_activate('fiddle')
+    Bundler.ui.level = bundler_ui_level if bundler_ui_level
   end
-
+  # For Ruby 3.4+, suppress a warning from `require 'fiddle'` when it's not in Gemfile.
+  verbose, $VERBOSE = $VERBOSE, nil
   require 'fiddle'
+  $VERBOSE = verbose
+
   require 'rbconfig/sizeof'
 
   unless Fiddle::SIZEOF_LONG == 8 and RbConfig::CONFIG["host_os"] =~ /linux|darwin/