Refactor: move "hPsi-call-act" procedure from `OperatorPW` into basic `Operator` and redesign `act()` interface

[maki49]

Background

Why move to basic class?

• for physics: act() is a basic property of an operator to a vector: $\ket{\psi_\text{out}}=\hat{O}\ket{\psi_\text{in}}$
• for demand:
  • LR-TDDFT Implementation #2460 has 2 different types of operators inheriting basic Operator rather than OperatorPW, whose act() interface will be called in hPsi() in sequence.
  • if a derived class (like OperatorLCAO) doesn't need the hPsi-call-act procedure, just ignore or override it.

Why redesign the interface?

The old act() inteface uses both psi::Psi<std::complex<FPTYPE>, Device> *psi_in and std::complex<FPTYPE>* tmpsi_in (the data pointer of psi_in) as input, which is a kind of redundancy.

What's changed (in #2912)

• move "hPsi-call-act" procedure from OperatorPW into basic Operator
• redesign act() interface:
  • hardware-friendly type:

  virtual void act(const int nbands,
        const int nbasis,
        const int npol,
        const FPTYPE* tmpsi_in,
        FPTYPE* tmhpsi,
        const int ngk_ik = 0)const;
  

  • developer-friendly type:

  virtual psi::Psi<FPTYPE> act(const psi::Psi<FPTYPE>& psi_in) const;
  

[mohanchen]

I agree.

[hongriTianqi]

• Identify the specific code file or section with the code quality issue.
• Investigate the issue and determine the root cause.
• Research best practices and potential solutions for the identified issue.
• Refactor the code to improve code quality, following the suggested solution.
• Ensure the refactored code adheres to the project's coding standards.
• Test the refactored code to ensure it functions as expected.
• Update any relevant documentation, if necessary.
• Submit a pull request with the refactored code and a description of the changes made.