ci: add Dart SDK tests to GitHub Actions workflow

Add Dart SDK test job to run tests on every push and PR. Includes:
- Dart stable SDK setup
- Pub cache for faster builds
- Test execution with expanded reporter for detailed output

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: mattsp1290

.github/workflows/test.yml

@@ -89,4 +89,33 @@ jobs:
 
     - name: Run tests
       working-directory: typescript-sdk
-      run: pnpm run test
+      run: pnpm run test
+
+  dart:
+    name: Dart SDK Tests
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v4
+
+    - name: Set up Dart
+      uses: dart-lang/setup-dart@v1
+      with:
+        sdk: stable
+
+    - name: Setup pub cache
+      uses: actions/cache@v4
+      with:
+        path: ~/.pub-cache
+        key: ${{ runner.os }}-dart-${{ hashFiles('**/pubspec.lock') }}
+        restore-keys: |
+          ${{ runner.os }}-dart-
+
+    - name: Install dependencies
+      working-directory: sdks/community/dart
+      run: dart pub get
+
+    - name: Run tests
+      working-directory: sdks/community/dart
+      run: dart test --reporter expanded