Add MatterSim and fix ASE cell convention issues.

[CompRhys]

• adds MatterSim (not all torch implementation as the neighbor list and triplet methods differ in strange ways).
• Reverts to use original SevenNet neighbor list based on covariate discussion with @AdeeshKolluru (c.f. mattersim neighbor list comment).
• defaults the neighbor list used for unbatched mace to match batched mace, update examples accordingly.
• parameterizes the contributed model tests adding structures with non-cubic cells. Fix column/row issues for some contributed models.
• parameterizes the elastic tests.
• Adds round trip tests for io models fixing column/row vector issues for converting into SimState.
• Adds properties for column and row vector cells, makes minimal changes to unitcell/frechet methods implementations due to column/row vector issues.

[CompRhys]

this is because volume isn't defined for PBC=False

[orionarcher]

This also won't be defined for PBC=False because state.cell will be None.

What about:

        half_supercell = (
            torch.max(state.volume) > 1000
            if state.pbc and self._half_supercell is None
            else self._half_supercell
        )