feat(metatomic): add symmetrization operations

xref: https://github.com/metatensor/metatomic/issues/114

Essentially from [metatomic-torch-v0.1.6](https://github.com/metatensor/metatomic/releases/tag/metatomic-torch-v0.1.6) onwards, ASE has an option to build rotationally averaged outputs from Metatomic models. This should be part of the potential here.