fix: resolve module name mismatch causing Integration Test failures on Windows

 **Critical Module Name Fixes:**
- Fix Rust PyO3 module name: change #[pymodule] fn demopy_gb_jj to #[pymodule] fn _rust
- Update Python module import: change from demopy_gb_jj._rust to demopy._rust
- Align module structure with maturin configuration: module-name = 'demopy._rust'
- Resolve PyInit symbol mismatch that prevented module import on Windows

 **Package Structure Alignment:**
- Package name: demopy_gb_jj (in pyproject.toml)
- Python module path: python/demopy/
- Rust module name: _rust (matches module-name config)
- Import statement: import demopy (works correctly)
- Rust extension import: demopy._rust (internal, automatic)

 **Comprehensive Integration Testing:**
- Create scripts/test_integration.py for complete package validation
- Test package import, functionality, wheel installation, and fallback behavior
- Verify both Rust extension and Python fallback implementations work correctly
- Add wheel installation testing in clean virtual environment

 **CI Workflow Improvements:**
- Update Integration Test workflow to properly test module import after build
- Fix fallback testing to use correct module name (demopy._rust instead of demopy_gb_jj._rust)
- Add comprehensive verification steps after maturin develop
- Include integration test execution in CI pipeline

 **Expected Resolution:**
- Integration Test workflow should complete successfully on all platforms (Ubuntu, Windows, macOS)
- maturin build should create wheels with correct module structure
- import demopy should work without ModuleNotFoundError
- Both Rust extension and Python fallback should function correctly
- All Python versions (3.8-3.13) should be supported

**Root Cause:** Module naming inconsistency between package name (demopy_gb_jj), Rust module name (demopy_gb_jj), expected module structure (demopy._rust), and actual import path (demopy). The PyO3 module name must match the module-name configuration in pyproject.toml.

**Solution:** Align all module names: Rust module  _rust, Python import  demopy._rust, maturin config  demopy._rust, maintaining backward compatibility with import demopy.

Author: jj-devhub

.github/workflows/ci.yml

@@ -173,8 +173,28 @@ jobs:
       shell: bash
       run: |
         source venv/bin/activate || source venv/Scripts/activate
+        echo "Building Rust extension with maturin..."
         maturin develop
 
+        # Verify the extension was built correctly
+        python -c "
+        try:
+            import demopy
+            print('✅ Successfully imported demopy')
+            print(f'Version: {demopy.__version__}')
+            hello_result = demopy.hello()
+            print(f'Hello: {hello_result}')
+            if 'Rust edition' in hello_result:
+                print('✅ Using Rust extension')
+            elif 'Python fallback' in hello_result:
+                print('✅ Using Python fallback')
+            else:
+                print(f'⚠️  Unknown implementation: {hello_result}')
+        except Exception as e:
+            print(f'❌ Import failed: {e}')
+            raise
+        "
+
     - name: Run Python tests
       shell: bash
       run: |
@@ -193,13 +213,25 @@ jobs:
         import builtins
         original_import = builtins.__import__
         def mock_import(name, *args, **kwargs):
-            if 'demopy_gb_jj._rust' in name:
-                raise ImportError('Mocked import error')
+            if 'demopy._rust' in name or '_rust' in name:
+                raise ImportError('Mocked import error for testing fallback')
             return original_import(name, *args, **kwargs)
         builtins.__import__ = mock_import
 
         import demopy
-        assert 'Python fallback' in demopy.hello()
+        hello_result = demopy.hello()
+        print(f'Fallback hello result: {hello_result}')
+        assert 'Python fallback' in hello_result, f'Expected Python fallback, got: {hello_result}'
         assert demopy.add(2, 3) == 5
-        print('Pure Python fallback test passed!')
+        assert demopy.multiply(2.5, 4.0) == 10.0
+        assert demopy.sum_list([1, 2, 3]) == 6
+        assert demopy.reverse_string('hello') == 'olleh'
+        assert demopy.power(2, 3) == 8
+        print('✅ Pure Python fallback test passed!')
         "
+
+    - name: Run integration tests
+      shell: bash
+      run: |
+        source venv/bin/activate || source venv/Scripts/activate
+        python scripts/test_integration.py

pyproject.toml

@@ -33,4 +33,5 @@ Issues = "https://github.com/jj-devhub/demopy/issues"
 [tool.maturin]
 features = ["pyo3/extension-module"]
 python-source = "python"
-module-name = "demopy_gb_jj._rust"
+# Map the Rust module to the correct Python module name
+module-name = "demopy._rust"

python/demopy/__init__.py

@@ -8,9 +8,10 @@
 
 try:
     # Import the Rust extension
-    from demopy_gb_jj._rust import add
-    from demopy_gb_jj._rust import hello as _rust_hello
-    from demopy_gb_jj._rust import multiply, power, reverse_string, sum_list
+    # When installed via maturin, the Rust module will be available as demopy._rust
+    from demopy._rust import add
+    from demopy._rust import hello as _rust_hello
+    from demopy._rust import multiply, power, reverse_string, sum_list
 
     # Use the Rust implementation for hello
     def hello():