[BE] Delete trailing whitespaces

[malfet]

In MPS ops. Also use nested namespaces, as since pytorch-2.4 this should
be a C++17 project

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/vision/9116

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✅ You can merge normally! (4 Unrelated Failures)

As of commit 8e7f21f with merge base d2db23a ():

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• CMake / windows (windows.g5.4xlarge.nvidia.gpu, cuda, 11.8) / windows-job (gh) (trunk failure)
  Process completed with exit code 1.
• Tests / unittests-macos (3.10, macos-m1-stable) / macos-job (gh) (trunk failure)
  test/test_ops.py::TestDeformConv::test_aot_dispatch_dynamic__test_forward[33-False-mps]
• Tests / unittests-macos (3.12, macos-m1-stable) / macos-job (gh) (trunk failure)
  test/test_ops.py::TestDeformConv::test_aot_dispatch_dynamic__test_forward[33-False-mps]
• Tests / unittests-macos (3.9, macos-m1-stable) / macos-job (gh) (trunk failure)
  test/test_ops.py::TestDeformConv::test_aot_dispatch_dynamic__test_forward[33-False-mps]

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