Improve function `pert_scaled`

[thangckt]

My suggestion:

• Separate VASP and ABACUS into separated functions (and may be separated files). This will helpful to someone who want to implement a new DFT engine and also convenient for maintain.

Summary by CodeRabbit

• New Features

  • Enhanced pert_scaled function to support different initialization styles ("VASP" or "ABACUS").

• Refactor

  • Improved loop logic and file handling for better performance and reliability in perturbation processes.