Add HQQ optimizer

[dacorvo]

What does this PR do?

This adds an HqqOptimizer that implements the algorithm described in "Half-Quadratic Quantization of Large Machine Learning Models", by Hicham Badri and Appu Shaji (https://mobiusml.github.io/hqq_blog/).
This is an adaption of the original implementation at https://github.com/mobiusml/hqq.

This optimizer is included more as an illustration than a real solution to address performance drop when quantizing models to qint4 or qint2, as it often produces models that achieve a worse performance than the ones produced by the vanilla MaxOptimizer (this confirms some numbers reported by several research papers).