Add MIFGSM Attack

[lcycode]

This code implements the fixed epsilon attack, MI-FGSM (https://openaccess.thecvf.com/content_cvpr_2018/html/Dong_Boosting_Adversarial_Attacks_CVPR_2018_paper.html).
MI-FGSM is a classic method that demonstrates superior and robust performance compared to PGD. It's worth noting that MI-FGSM serves as a baseline for many SOTA research papers. Therefore, implementing MI-FGSM proves to be a convenient choice for researchers. Please feel free to share any suggestions for further improvements to the code.

(I close the last request, because I rebase the code by mistakes.)

[lcycode]

I've incorporated the test code and successfully passed checks such as black, flake8, and mypy. I hop that these could be beneficial to you.

[coveralls]

coverage: 98.47% (+0.02%) from 98.455%
when pulling 72f3381 on lcycode:add_mifgsm_attack
into 475cb98 on bethgelab:master.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.46%. Comparing base (475cb98) to head (72f3381).
Report is 14 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #717      +/-   ##
==========================================
+ Coverage   98.45%   98.46%   +0.01%     
==========================================
  Files          55       56       +1     
  Lines        3495     3529      +34     
==========================================
+ Hits         3441     3475      +34     
  Misses         54       54              

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[zimmerrol]

LGTM