Reimplement cell_to_cellpar in torchsim

[thomasloux]

cell_to_cellpar is used in Orb: https://github.com/TorchSim/torch-sim/blob/main/torch_sim/models/orb.py#L185

Currently TorchSim transfers the cell to numpy to use the function before transferring it back to torch.

Just need to turn this numpy code into torch: https://ase-lib.org/_modules/ase/geometry/cell.html

[wwymak]

Hi, I can have a go at this if no one else is working on it yet? Also are there conventions on the dev workflow (e.g. extra things to setup locally for dev?)

[thomasloux]

Yes: https://github.com/TorchSim/torch-sim/blob/main/docs/dev/dev_install.md (add prek to check before commit)
But overall: run ruff and pytest.
And add a test to check that your implement is correct.
WARNING: cell convention is not the same between ASE and TorchSim (cell vectors in row / columns)

[orionarcher]

WARNING: cell convention is not the same between ASE and TorchSim (cell vectors in row / columns)

Honestly this is probably worth calling out somewhere.