Benchmarking the implementations

[mitkotak]

Really cool work ! Was interested in benchmarking the CG tensor product machinery against e3nn code and see if there are any ideas that can be integrated. Can you point me to the equivalent of https://docs.e3nn.org/en/stable/api/o3/o3_tp.html#e3nn.o3.FullTensorProduct ? I can use that as an anchor point to explore the rest of the repo. Thanks again for putting out the code !