[FSDP][BE] Improve `device_id` + CPU offload test (#92031)
Closes https://github.com/pytorch/pytorch/issues/83054. The new version of the test ensures that the parent FSDP instance has managed parameters to trigger the `module.to(device_from_device_id)` call, which moves the child FSDP instance's managed parameters (and hence must be hackily moved back).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/92031
Approved by: https://github.com/zhaojuanmao, https://github.com/rohan-varma
