Centralize Ruby Version to .ruby-version

The `.ruby-version` file is the ecosystem standard for defining a Ruby version.  This PR adds the `.ruby-version` file, ensures a `required_ruby_version` is set, and removes all other references to Ruby in this repository, aligning it with the standard.
> [!IMPORTANT]
> Please verify the following before merging:

Verify that the changes in the PR meets the following requirements or adjust manually to make it compliant:
  - [ ] `.ruby-version` file is present with the correct Ruby version defined
  - [ ] A `required_ruby_version` in your gemspec is set
  - [ ] There is no Ruby version present in the  `dev.yml` Ruby task (before: `- ruby: x.x.x`, after: `- ruby`)
  - [ ] There is no Ruby version/requirement referenced in the `Gemfile` (no lines with `ruby  <some-version>`)
  - [ ] A `Gemfile.lock` is built with the defined Ruby version
  - [ ] The version of Rubocop installed is 1.61.0 or greater
  - [ ] There is no `TargetRubyVersion` defined  in `rubocop.yml` (reads from  `required_ruby_version` on Rubocop 1.61.0)
  - [ ] There is no Ruby argument  present in  `ruby/setup-ruby` Github Actions that do **not**  run on a Ruby matrix (no lines with `ruby-version: “x.x”`)

To establish consistency, the `required_ruby_version`is set to 2.7. If you think that another version is a better fit, please make the applicable changes.

Please merge this PR if it looks good, this PR will be addressed if there isn't any activity after 4 weeks.

.github/workflows/ci.yml

@@ -0,0 +1,24 @@
+name: CI
+on:
+  pull_request:
+    branches:
+      - '**'
+  push:
+    branches:
+      - master
+jobs:
+  build:
+    name: Ruby ${{ matrix.version }}
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        version: [ '2.7', '3.0', '3.1', '3.2', '3.3' ]
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Ruby ${{ matrix.version }}
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.version }}
+          bundler-cache: true
+      - name: Test
+        run: bundle exec rake test

.gitignore

@@ -2,4 +2,3 @@ pkg/*
 *.gem
 .bundle
 .DS_Store
-Gemfile.lock

.ruby-version

@@ -0,0 +1 @@
+2.7.5

Gemfile.lock

@@ -0,0 +1,49 @@
+PATH
+  remote: .
+  specs:
+    active_utils (3.4.1)
+      activesupport (>= 4.2)
+      i18n
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    activesupport (7.1.3.2)
+      base64
+      bigdecimal
+      concurrent-ruby (~> 1.0, >= 1.0.2)
+      connection_pool (>= 2.2.5)
+      drb
+      i18n (>= 1.6, < 2)
+      minitest (>= 5.1)
+      mutex_m
+      tzinfo (~> 2.0)
+    base64 (0.2.0)
+    bigdecimal (3.1.7)
+    concurrent-ruby (1.2.3)
+    connection_pool (2.4.1)
+    drb (2.2.1)
+    i18n (1.14.4)
+      concurrent-ruby (~> 1.0)
+    minitest (5.22.3)
+    mocha (2.1.0)
+      ruby2_keywords (>= 0.0.5)
+    mutex_m (0.2.0)
+    rake (13.2.0)
+    ruby2_keywords (0.0.5)
+    tzinfo (2.0.6)
+      concurrent-ruby (~> 1.0)
+
+PLATFORMS
+  arm64-darwin-21
+  arm64-darwin-23
+  x86_64-linux
+
+DEPENDENCIES
+  active_utils!
+  minitest
+  mocha
+  rake
+
+BUNDLED WITH
+   2.4.18

active_utils.gemspec

@@ -12,6 +12,8 @@ Gem::Specification.new do |s|
   s.summary     = %q{Common utils used by active_merchant, active_fulfillment, and active_shipping}
   s.license     = 'MIT'
 
+  s.required_ruby_version = ">= 2.7"
+
   s.rubyforge_project = "active_utils"
 
   s.add_dependency('activesupport', '>= 4.2')