Added ruby_memcheck [skip ci]

Author: ankane

Gemfile

@@ -9,3 +9,4 @@ gem "matrix"
 gem "numo-narray", platform: [:mri, :windows]
 gem "rover-df", platform: [:mri, :windows]
 gem "csv"
+gem "ruby_memcheck"

Rakefile

@@ -1,10 +1,16 @@
 require "bundler/gem_tasks"
 require "rake/testtask"
+require "ruby_memcheck"
 
-Rake::TestTask.new do |t|
+test_config = lambda do |t|
   t.pattern = "test/**/*_test.rb"
   t.warning = false # for daru
 end
+Rake::TestTask.new(&test_config)
+
+namespace :test do
+  RubyMemcheck::TestTask.new(:valgrind, &test_config)
+end
 
 task default: :test