fix: require set for Ruby 3.1 compatibility

yhk1038 · yhk1038 · commit 5e12f0648d4a · 2025-12-29T07:59:27.000+09:00
diff --git a/lib/t_ruby/parser_combinator/token/expression_parser.rb b/lib/t_ruby/parser_combinator/token/expression_parser.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "set"
+
 module TRuby
   module ParserCombinator
     # Expression Parser - Parse expressions into IR nodes
