Fix pipe tests failures on CPU (#8611)
Follow up #8381 @delock
fix
```
unit/pipe/test_pipe_module.py
unit/runtime/pipe/test_pipe.py
```
This pull request refactors device handling in the activation
checkpointing code to simplify and standardize how device variables are
used. The main change is to consistently use a `device` variable instead
of `cuda_device` and to remove unused or redundant stream-related code.
This improves code clarity and maintainability without changing
functionality.
**Device handling simplification:**
* Replaced all occurrences of `cuda_device` with a unified `device`
variable obtained from `get_accelerator().current_device_name()` in
`checkpointing.py`.
[[1]](diffhunk://#diff-a4333224075c38d4a6f6aa97123c10f93e519b39cce1f02ecaa55d881493bb2dL604-R604)
[[2]](diffhunk://#diff-a4333224075c38d4a6f6aa97123c10f93e519b39cce1f02ecaa55d881493bb2dL838-R831)
[[3]](diffhunk://#diff-a4333224075c38d4a6f6aa97123c10f93e519b39cce1f02ecaa55d881493bb2dL941-R933)
* Updated all device argument usages in calls to `copy_to_device`,
`gather_partitioned_activations`, and `move_to_device` to use the new
`device` variable.
[[1]](diffhunk://#diff-a4333224075c38d4a6f6aa97123c10f93e519b39cce1f02ecaa55d881493bb2dL618-R617)
[[2]](diffhunk://#diff-a4333224075c38d4a6f6aa97123c10f93e519b39cce1f02ecaa55d881493bb2dL709-R714)
[[3]](diffhunk://#diff-a4333224075c38d4a6f6aa97123c10f93e519b39cce1f02ecaa55d881493bb2dL851-R843)
[[4]](diffhunk://#diff-a4333224075c38d4a6f6aa97123c10f93e519b39cce1f02ecaa55d881493bb2dL952-R950)
**Stream and code cleanup:**
* Removed creation and usage of the `transport_stream` variable, and
deleted commented-out or unused stream synchronization code.
These changes make the device management more straightforward and reduce
potential confusion around device and stream handling in activation
checkpointing.
Signed-off-by: Jin, Youzhi <youzhi.jin@intel.com>
