Fix CI: Update poetry.lock and fix dependency conflicts

- Update pytest to ^8.0.0 (required by pytest-httpx)
- Update pytest-httpx to >=0.30.0 (compatible with httpx 0.28.1)
- Update langgraph to ^1.0.0 (required by langchain 1.x)
- Regenerate poetry.lock

Author: fede-kamel