Utility function for rotation of equivariant TensorMaps

[MichelangeloDomina]

We would like to have a public functionality to rotate equivariant tensors in a TensorMap format. We already have a basic functionality for testing purposes in the CG submodule but the intention would be to make this public.

Something like (as suggested by @Luthaf):

class WignerDReal:
    def __init__(self, max_angular):
        ...

    def rotation(self, angles) -> RotationMatrix:
        ...

class RotationMatrix:
    def __init__(self, ...):
        ...

    def rotate_tensor(self, tensor: TensorMap) -> TensorMap:
        ...

    def rotate_block(self, o3_lamda: int, o3_sigma: int, block: TensorBlock) -> TensorBlock:
        ...

In the future, the WignerDReal class will be abstracted to the wigners package and/or custom implementation for lower max_angular could be written.

Tagging people involved: @jwa7 , @Luthaf