`openmm-ml` compatibility for generic `MultiStateSampler` objects

[dominicrufa]

Description

implement compatibility for openmm-ml (and openmm 8/beta) to allow for generic MultiStateSampler free energy/sampling calculations.

Todos

• [ ] Implement feature / fix bug
• [ ] Add tests
• [ ] Update documentation as needed
• [ ] Update changelogNotable points that this PR has either accomplished or will accomplish.

Status

• [ ] Ready to go

[codecov[bot]]

Codecov Report

Merging #598 (389531b) into main (b379af3) will decrease coverage by 0.56%. The diff coverage is 14.60%.