Adjusted MCLMC

[reubenharry]

A change is also made to partially_refresh_momentum, which allows (adjusted) MCHMC to be the limit of MCLMC with infinite $L$. This is convenient since the user may or not want partial refreshment (in the unadjusted case, we find that it is always beneficial, but don't know yet in the adjusted case)

Addresses #676.

Checklist:

• If I add a new sampler, there is an issue discussing it already;
• We should be able to understand what the PR does from its title only;
• There is a high-level description of the changes;
• There are links to all the relevant issues, discussions and PRs;
• The branch is rebased on the latest main commit;
• Commit messages follow these guidelines;
• The code respects the current naming conventions;
• Docstrings follow the numpy style guide
• pre-commit is installed and configured on your machine, and you ran it before opening the PR;
• There are tests covering the changes;
• The doc is up-to-date;
• If I add a new sampler* I added/updated related examples

[reubenharry]

I think this is ready to review again @junpenglao

EDIT: actually, let me first update the tuning algorithm.

[reubenharry]

@junpenglao Now ready to review! I will extend the sampling book's MCLMC section with the adjusted option shortly.

[junpenglao]

Minor nits only.

[junpenglao]

Thank you!