Implement spectrum adaptive KPM method

[tchen01]

I've recently done some work on the kernel polynomial method https://arxiv.org/abs/2308.15683. The main idea is that in lots of settings it makes sense to implement the KPM using Lanczos so that it can adapt to the spectrum.

I wonder if this is something that might be relevant for Quantica? I have a python implementation: https://github.com/tchen-research/spectral_density.