Enable Frozen String Literals (#42)

Add `frozen_string_literal` magic comment to enable frozen string
literals for Ruby versions that support it to prepare the library
for Ruby 4, ensuring all specs pass and referencing community guidance.

This change reduces allocations on Ruby 2.3 and newer, and despite
initial concerns, benchmarks during testing show no evidence of
regression.

Since the library still supports Ruby versions earlier than 2.3 and
potential issues cannot be ruled out for those versions, the CI workflow
now sets

```
RUBYOPT='--enable=frozen-string-literal --debug=frozen-string-literal'
```

to help prevent future regressions.

Code has been automatically fixed by RuboCop by temporarily change
target version to 2.3 and running:

```
be rubocop --only Style/FrozenStringLiteralComment,Layout/EmptyLineAfterMagicComment,Style/RedundantFreeze,Style/MutableConstant -A lib/**/*.rb
```

Close #41

Author: tagliala

.github/workflows/tests.yml

@@ -10,6 +10,11 @@ jobs:
       matrix:
         ruby: [ '3.1', '3.2', '3.3', '3.4', 'ruby-head' ]
 
+    env:
+      # The RUBYOPT flags can be removed if RuboCop style checks are added
+      # to the lint workflow and support for Ruby < 2.3 is dropped.
+      RUBYOPT: '--enable=frozen-string-literal --debug=frozen-string-literal'
+
     steps:
       - uses: actions/checkout@v4
       - name: Set up Ruby ${{ matrix.ruby }}
@@ -21,4 +26,4 @@ jobs:
       - name: Test with Rake
         run: bundle exec rake
       - uses: codecov/codecov-action@v3
-        if: matrix.ruby == '3.4' # match version in spec_helper.rb:1
+        if: matrix.ruby == '3.4' # match version in spec_helper.rb:3

CHANGELOG.md

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 source 'https://rubygems.org'
 
 # Specify your gem's dependencies in js_regex.gemspec

Gemfile

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 Dir['tasks/**/*.rake'].each { |file| load(file) }
 
 require 'bundler/gem_tasks'

Rakefile

@@ -1,4 +1,5 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
 
 require 'bundler/setup'
 require 'js_regex'

bin/console

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 dir = File.expand_path(__dir__)
 require File.join(dir, 'lib', 'js_regex', 'version')
 

js_regex.gemspec

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # JsRegex converts ::Regexp instances to JavaScript.
 #
 # Usage:

lib/js_regex.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class JsRegex
   #
   # This class acts as a facade, passing a Regexp to the Converters.

lib/js_regex/conversion.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class JsRegex
   module Converter
     Dir[File.join(__dir__, 'converter', '*.rb')].sort.each do |file|

lib/js_regex/converter.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative 'base'
 
 class JsRegex