🧪 Add cross-platform testing matrix

- Test across Linux, Windows, and macOS
- Maintain Ruby 2.7-3.3 testing on all platforms
- Optimize coverage/RuboCop to run only on Ubuntu + Ruby 3.3
- Ensure gem works reliably across different operating systems
- Total test matrix: 15 combinations (3 OS × 5 Ruby versions)

Author: voltechs

.github/workflows/ci.yml

@@ -14,11 +14,12 @@ permissions:
 
 jobs:
   test:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
 
     strategy:
       fail-fast: false
       matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
         ruby-version: ["2.7", "3.0", "3.1", "3.2", "3.3"]
 
     steps:
@@ -36,16 +37,16 @@ jobs:
       - name: Run tests with coverage
         run: bundle exec rspec
 
-      - name: Upload coverage artifact (Ruby 3.3 only)
-        if: matrix.ruby-version == '3.3'
+      - name: Upload coverage artifact (Ruby 3.3 on Ubuntu only)
+        if: matrix.ruby-version == '3.3' && matrix.os == 'ubuntu-latest'
         uses: actions/upload-artifact@v4
         with:
           name: coverage-report
           path: coverage/
           retention-days: 1
 
-      - name: Run RuboCop (Ruby 3.3 only)
-        if: matrix.ruby-version == '3.3'
+      - name: Run RuboCop (Ruby 3.3 on Ubuntu only)
+        if: matrix.ruby-version == '3.3' && matrix.os == 'ubuntu-latest'
         run: bundle exec rubocop || true
         continue-on-error: true