chore: Update RuboCop TargetRubyVersion to 3.2

Align RuboCop TargetRubyVersion with gemspec's required_ruby_version.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.rubocop.yml

@@ -13,7 +13,7 @@ inherit_mode:
 
 AllCops:
   NewCops: enable
-  TargetRubyVersion: 3.0
+  TargetRubyVersion: 3.2
   SuggestExtensions: false
   DisplayCopNames: true
   CacheRootDirectory: tmp/rubocop-cache