Support for permutational index symmetry

[Krzmbrzl]

In https://github.com/Jutho/TensorKit.jl/issues/50#issuecomment-830868009 I found

symmetries under index permutations are currently not supported. In general, it's quite hard to take them into account, in particular in a way that leads to a large speedup.

I just wanted to come back to it (given that this statement is from 2021) and ask: Has there been any work in this direction in the meantime?

FWIW I think already support in the sense of figuring out that if $f_{ab} = f_{ba}$, then it is enough to compute and store the elements for $b > a$ (which especially for higher-dimensional tensors can lead to significant memory and also processing time savings).