Feat (function): Fourier-based gradient approximation for Round

[Giuseppe5]

Reason for this PR

Implement StableQAT from https://github.com/microsoft/StableQAT/
Tested on:

python bnn_pynq_train.py --network CNV_2W2A --epochs 20

Model	Test Accuracy
STE	70.440
RDFS	69.050

Testing Summary

TBD

Risk Highlight

• This PR includes code from another work (please detail).
• This PR contains API-breaking changes.
• This PR depends on work in another PR (please provide links/details).
• This PR introduces new dependencies (please detail).
• There are coverage gaps not covered by tests.
• Documentation updates required in subsequent PR.