Setup ruby_memcheck

Hoping it might find the leak reported in ruby#460

.github/workflows/ci.yml

@@ -56,3 +56,26 @@ jobs:
 
       - run: gem install pkg/*.gem
         if: ${{ matrix.ruby != '3.2' }}
+
+  valgrind:
+    name: Ruby memcheck
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Set up Ruby
+        uses: ruby/setup-ruby-pkgs@v1
+        with:
+          ruby-version: "3.3"
+          apt-get: ragel valgrind
+
+      - run: |
+          bundle config --without benchmark
+          bundle install
+
+      - run: rake compile
+
+      - run: rake valgrind

Gemfile

@@ -7,6 +7,7 @@ else
 end
 
 group :development do
+  gem "ruby_memcheck"
   gem "ostruct"
   gem "rake"
   gem "rake-compiler"

Rakefile

@@ -1,3 +1,5 @@
+require "ruby_memcheck"
+
 begin
   require 'rubygems/package_task'
 rescue LoadError
@@ -250,6 +252,12 @@ else
     t.options = '-v'
   end
 
+  RubyMemcheck::TestTask.new(valgrind: [ :set_env_ext, :check_env, :compile, :do_test_ext ]) do |t|
+    t.test_files = FileList['test/json/*_test.rb']
+    t.verbose = true
+    t.options = '-v'
+  end
+
   desc "Update the tags file"
   task :tags do
     system 'ctags', *Dir['**/*.{rb,c,h,java}']