refactor: improve test structure and fix main_cli example

- Move pytest configuration from pytest.ini to pyproject.toml
- Remove unnecessary run_tests.py script (use test extras instead)
- Fix main_cli_example.py to properly use command line arguments for LLM config
- Add test_readme_examples.py to test code examples from README
- Refactor tests to use pytest fixtures and parametrization
- Update test documentation to reflect new structure
- Set proper environment variables in CI for test execution

tests/test_basic.py

@@ -0,0 +1,86 @@
+"""
+Basic functionality tests for CI pipeline using pytest.
+"""
+
+import tempfile
+from pathlib import Path
+
+import pytest
+
+
+def test_imports():
+    """Test that all packages can be imported."""
+
+    # Test C++ extensions
+
+
+@pytest.mark.parametrize("backend_name", ["hnsw", "diskann"])
+def test_backend_basic(backend_name):
+    """Test basic functionality for each backend."""
+    from leann.api import LeannBuilder, LeannSearcher
+
+    # Create temporary directory for index
+    with tempfile.TemporaryDirectory() as temp_dir:
+        index_path = str(Path(temp_dir) / f"test.{backend_name}")
+
+        # Test with small data
+        texts = [f"This is document {i} about topic {i % 5}" for i in range(100)]
+
+        # Configure builder based on backend
+        if backend_name == "hnsw":
+            builder = LeannBuilder(
+                backend_name="hnsw",
+                embedding_model="facebook/contriever",
+                embedding_mode="sentence-transformers",
+                M=16,
+                efConstruction=200,
+            )
+        else:  # diskann
+            builder = LeannBuilder(
+                backend_name="diskann",
+                embedding_model="facebook/contriever",
+                embedding_mode="sentence-transformers",
+                num_neighbors=32,
+                search_list_size=50,
+            )
+
+        # Add texts
+        for text in texts:
+            builder.add_text(text)
+
+        # Build index
+        builder.build_index(index_path)
+
+        # Test search
+        searcher = LeannSearcher(index_path)
+        results = searcher.search(["document about topic 2"], top_k=5)
+
+        # Verify results
+        assert len(results) > 0
+        assert len(results[0]) > 0
+        assert "topic 2" in results[0][0].text or "document" in results[0][0].text
+
+
+@pytest.mark.skipif("sys.platform == 'darwin'", reason="May fail on macOS due to C++ ABI issues")
+def test_large_index():
+    """Test with larger dataset (skip on macOS CI)."""
+    from leann.api import LeannBuilder, LeannSearcher
+
+    with tempfile.TemporaryDirectory() as temp_dir:
+        index_path = str(Path(temp_dir) / "test_large.hnsw")
+        texts = [f"Document {i}: {' '.join([f'word{j}' for j in range(50)])}" for i in range(1000)]
+
+        builder = LeannBuilder(
+            backend_name="hnsw",
+            embedding_model="facebook/contriever",
+            embedding_mode="sentence-transformers",
+        )
+
+        for text in texts:
+            builder.add_text(text)
+
+        builder.build_index(index_path)
+
+        searcher = LeannSearcher(index_path)
+        results = searcher.search(["word10 word20"], top_k=10)
+        assert len(results[0]) == 10