Set PyMBAR solver to "robust" and use PyMBAR4

[hannahbaumann]

Checklist

• [ ] Added a news entry

Developers certificate of origin

• [x] I certify that this contribution is covered by the MIT License here and the Developer Certificate of Origin at https://developercertificate.org/.

[pep8speaks]

Hello @hannahbaumann! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers:

Comment last updated at 2024-06-17 10:29:20 UTC

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.47%. Comparing base (76af603) to head (a92d517).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #871 +/- ## ========================================== - Coverage 94.08% 91.47% -2.62% ========================================== Files 134 134 Lines 9790 9790 ========================================== - Hits 9211 8955 -256 - Misses 579 835 +256 ``` | [Flag](https://app.codecov.io/gh/OpenFreeEnergy/openfe/pull/871/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy) | Coverage Δ | | |---|---|---| | [fast-tests](https://app.codecov.io/gh/OpenFreeEnergy/openfe/pull/871/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy) | `91.47% <100.00%> (?)` | | | [slow-tests](https://app.codecov.io/gh/OpenFreeEnergy/openfe/pull/871/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy#carryforward-flags-in-the-pull-request-comment) to find out more.

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[mikemhenry]

IMHO this should get a news entry since this change could cause a system to go from working to not working.

[IAlibay]

IMHO this should get a news entry since this change could cause a system to go from working to not working.

Agreed - this is more of a proof of concept at the moment, @RiesBen is taking over testing for this. We'll need to do a few PLB systems to convince ourselves that this works.