Add Adam Optimizer

[clpetix]

This PR implements the Adam Optimizer. We've had enough success with this in several projects that I think it is worth adding it as an option!

[mphoward]

Looks great! Here are a couple minor requests.

[clpetix]

@mphoward, whenever you have a chance could you look at these failing jobs and see if you have any ideas? I don't really understand what is happening but I think it has to just be a GitHub actions issue 😅

[mphoward]

It is surprisingly hard to spot, but based on this error:

Defaulting to user installation because normal site-packages is not writeable

I suspect that the problem is that a different pip is being used (ex: the system one), and so the tests are choking on those dependencies. I am not sure if relentless is even installed in the test environment!

I'm not sure why this is broken all of a sudden. As a quick fix, you could try explicitly adding pip as the last package installed when HOOMD / LAMMPS are installed via conda:

https://www.anaconda.com/docs/getting-started/working-with-conda/packages/pip-install#using-pip-install-in-a-conda-environment

If that doesn't work, I have been considering moving to pixi because it is able to solve conda-forge and PyPI dependencies simultaneously (even on my desktop). That will be more work though.

[clpetix]

I've addressed all your comments, and this should be about ready to go!

[mphoward]

Thank you, looks great!