Skip optional-dependency test modules instead of erroring at collection

[rogerSuperBuilderAlpha]

Problem

test/test_cache.py and test/test_parallel.py import their optional dependencies at module scope:

import redis   # test_cache.py
import ray      # test_parallel.py

redis and ray are optional extras (caching and parallel). On any environment that doesn't have them installed, a plain pytest run aborts during collection:

ERROR test/test_parallel.py - ModuleNotFoundError: No module named 'ray'
ERROR test/test_cache.py
!!!!!!!!!!!!!!!!!!! Interrupted: errors during collection !!!!!!!!!!!!!!!!!!!!

Because collection errors are fatal, this masks the entire rest of the suite for a contributor who installed only .[dev].

Change

Use pytest.importorskip for the optional imports so the modules skip cleanly when the dependency is missing, while still running fully where the extras are installed (e.g. CI):

redis = pytest.importorskip("redis")
ray = pytest.importorskip("ray")

Verification

• With neither extra installed, pytest --co now collects the full suite with no collection errors (previously 4), and the two modules report as skipped rather than error.
• Where redis/ray are installed, behavior is unchanged (the import resolves and the tests run as before).