Will/Non-TPU dependent Integration with Aether

[wz-ml]

Integrations with the Aether repository before the monorepo merge.

Additions:

• Modifications to permit Aether to use Devinterp functions:
  • LLCEstimator (src/devinterp/slt/llc.py)
  • OnlineLLCEstimator (src/devinterp/slt/llc.py)
  • SGLD (src/devinterp/optim/sgld.py)
• A few behavior-preserving modifications that I hope un-curses the code a little.

[svwingerden]

After some bugfixes, all tests (except acc/ord) now pass. But there are a few small issues:

1. Please remove george's sampling method code, and add it into its own separate branch (no pr needed)
2. Please update OnlineLLCEstimator to also take in both nbeta and temperature, like was done for LLCEstimator
3. Please update the example notebooks to adjust for the made changes. (I've fixed introduction.ipynb and normal_crossing.ipynb already)

[wz-ml]

Check on changes 1, 2, and partly 3. I've updated all the notebooks except for the two mentioned and made minor fixes to callbacks. All of them should be working except for diagnostics.ipynb, which I've updated but is blocked on the default init_loss not being implemented for OnlineLLCEstimator. Merge at your leisure : )