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

pyproject.toml

@@ -49,6 +49,7 @@ dependencies = [
 dev = [
     "pytest>=7.0",
     "pytest-cov>=4.0",
+    "pytest-xdist>=3.0",  # For parallel test execution
     "black>=23.0",
     "ruff>=0.1.0",
     "matplotlib",
@@ -56,6 +57,15 @@ dev = [
     "pre-commit>=3.5.0",
 ]
 
+test = [
+    "pytest>=7.0",
+    "pytest-timeout>=2.0",
+    "llama-index-core>=0.12.0",
+    "llama-index-readers-file>=0.4.0",
+    "python-dotenv>=1.0.0",
+    "sentence-transformers>=2.2.0",
+]
+
 diskann = [
     "leann-backend-diskann",
 ]
@@ -123,3 +133,24 @@ line-ending = "auto"
 dev = [
     "ruff>=0.12.4",
 ]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+python_files = ["test_*.py"]
+python_classes = ["Test*"]
+python_functions = ["test_*"]
+markers = [
+    "slow: marks tests as slow (deselect with '-m \"not slow\"')",
+    "openai: marks tests that require OpenAI API key",
+]
+timeout = 600
+addopts = [
+    "-v",
+    "--tb=short",
+    "--strict-markers",
+    "--disable-warnings",
+]
+env = [
+    "HF_HUB_DISABLE_SYMLINKS=1",
+    "TOKENIZERS_PARALLELISM=false",
+]