- Replace OnspringApiSdk package with onspring_api_sdk package
- Add sync (OnspringClient) and async (AsyncOnspringClient) clients
- Migrate from requests to httpx for HTTP transport
- Migrate from raw dataclasses to Pydantic v2 models with alias support
- Add shared response handler module (_responses.py) to reduce duplication
- Add typed exceptions (OnspringError, OnspringAuthenticationError, etc.)
- Preserve full API coverage for apps, fields, files, lists, records, and reports
