Improving the MLP example.

[drivanov]

Description

Changes were made in accordance with the CPU best practices for DGL. By doing this, we resolved the following warning:

/usr/local/lib/python3.10/dist-packages/dgl/dataloading/dataloader.py:1149: DGLWarning: Dataloader CPU affinity opt is not enabled, consider switching it on (see enable_cpu_affinity() or CPU best practices for DGL [https://docs.dgl.ai/tutorials/cpu/cpu_best_practises.html])
  dgl_warning(

and improved the training run time. For 5 epochs, the execution time improvement is:

         Before:           After:
real    4m39.307s        0m28.892s
user    3m59.116s        1m55.143s
sys     1m16.790s        0m58.011s

Checklist

Please feel free to remove inapplicable items for your PR.

• I've leverage the tools to beautify the python and c++ code.
• The PR is complete and small, read the Google eng practice (CL equals to PR) to understand more about small PR. In DGL, we consider PRs with less than 200 lines of core code change are small (example, test and documentation could be exempted).
• To the best of my knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

Changes

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Commit ID: 7a350af

Build ID: 1

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