Add square-symmetry augmentations and sampling fixes

[JiamingPan]

Summary:

• add RandomRot90 and RandomDihedral2D augmentations for square-symmetry physics augmentation
• keep RandomFlip config dims as a tuple and add augmentation unit tests
• make sampling compatible with schedulers whose step() does not accept generator, avoid duplicate EMA symlink failures, and unwrap synthesized EMA models before sampling

Notes:

• This is intended for CAMELS-style scalar maps where rotations/flips are physical symmetries and should not change the field distribution.
• I could not run full pytest locally because this machine lacks torch/pytest; please run the existing test suite in the normal cosmo_diffusion environment or CI before merging.

[nkern]

thanks for the addition jiaming--will have a look and give comments. fyi--the CI automatically runs pytest and can import torch, and it looks like it passes! but will leave some comments before we merge

[nkern]

looks fine to me--just a quick question about the ema_model, otherwise looks good!