Staging integration tests require redis just to import top-level conftest

[anth-volk]

Problem

The staging integration-test job runs only deployed-service tests:

• tests/integration/test_live_calculate.py
• tests/integration/test_live_economy.py

But pytest still imports the top-level tests/conftest.py, and that file imports redis at module import time.

The workflow step currently installs only:

• pytest
• httpx

So test collection fails before any integration test runs with:

ImportError while loading conftest '/home/runner/work/policyengine-api/policyengine-api/tests/conftest.py'.
tests/conftest.py:6: in <module>
    import redis
E   ModuleNotFoundError: No module named 'redis'

Root cause

redis is only needed by the rest_client fixture, not by the deployed-service integration tests. But because it is imported eagerly at module import time, every test tier under tests/ inherits that dependency.

Fix

Import redis lazily inside the rest_client fixture so only tests that actually use that fixture require the package.