Integration testing for Ray runner initialization

[kevinzwang]

This would involve spinning up a Ray cluster in a container that Daft would connect to. Several paths to test:

• [ ] ray.init() not called, daft.context.set_runner_ray() called with local cluster
• [ ] ray.init() not called, daft.context.set_runner_ray() called with remote cluster and RAY_ADDRESS envvar set
• [ ] ray.init() not called, daft.context.set_runner_ray(address="...") called with remote cluster
• [ ] ray.init() called with local cluster, daft.context.set_runner_ray() called and should connect to cluster
• [ ] ray.init() called with local cluster, daft.context.set_runner_ray(address="...") called and should ignore address
• [ ] ray.init() called with remote cluster, daft.context.set_runner_ray() called and should connect to cluster
• [ ] ray.init() called with remote cluster, daft.context.set_runner_ray(address="...") called and should ignore address