Enable GPU->CPU transfers

[mzient]

Category:

New feature Refactoring

Description:

GPU->CPU transfer is made possible via .cpu() function in DataNode. Some refactoring of pipeline class. The checks have been removed from Pipeline class. The old executor still raises an error when GPU->CPU transfer occurs.

Additional information:

Affected modules and functionalities:

Key points relevant for the review:

Some old tests were removed or reduced to allow for the new capability.

• [ ] Existing tests apply
• [X] New tests added
  • [X] Python tests
  • [ ] GTests
  • [ ] Benchmark
  • [ ] Other
• [ ] N/A

Checklist

Documentation

• [ ] Existing documentation applies
• [ ] Documentation updated
  • [ ] Docstring
  • [ ] Doxygen
  • [ ] RST
  • [ ] Jupyter
  • [ ] Other
• [ ] N/A

DALI team only

Requirements

• [X] Implements new requirements
• [ ] Affects existing requirements
• [ ] N/A EXE.06

REQ IDs: N/A

JIRA TASK: N/A