chore(python-sdk): lock pyqwest 0.8.0

The branch's pyproject already requires `pyqwest>=0.8.0,<0.9` for the Proxy
object and the multipart fix; refresh the lockfile now that 0.8.0 is on PyPI.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: mishushakov