Refactor: Simplify some functions in DeePKS.

[ErjieWu]

Linked Issue

Fix #6075

What's changed?

• Add ticks in update_dmr() and double check the place it is used in DeePKS to avoid repeating calculations.
• Use slice() method in torch::Tensor to simplify the code.
• Combine the repeating loop for stress and force calculations in DeePKS.

[ErjieWu]

Note: The integrate test 204_NO_KP_NC (non-collinear Fe Anti-ferromagnetic and lcao basis calculation) results are different in runs and I'm not sure whether this is normal.