feat: Add Booklooker client configuration and exception handling

- Introduced BooklookerConfig class for runtime configuration management.
- Created custom exceptions for API errors, including authentication and validation errors.
- Generated API contracts from OpenAPI specification, including endpoints and security schemes.
- Implemented models for articles, orders, and webhooks to facilitate data handling.
- Developed a webhook helper for processing and enriching webhook events.
- Added tests for configuration defaults, token expiration, and webhook enrichment.

.gitignore

@@ -0,0 +1,9 @@
+__pycache__/
+.pytest_cache/
+*.pyc
+*.pyo
+*.pyd
+.venv/
+dist/
+build/
+*.egg-info/