[source_hsolver] `source_hsolver` should not depend on `source_pw`

[Critsium-xy]

Describe the Code Quality Issue

Description

source_hsolver includes concrete plane-wave Hamiltonian implementations from
source_pw, violating the target dependency boundary.

Locations

Production code (2 files):

• hsolver_lcaopw.cpp → source_pw/module_pwdft/hamilt_pw.h, source_pw/module_pwdft/hamilt_lcaopw.h
• hsolver_pw_sdft.h → source_pw/module_stodft/hamilt_sdft_pw.h, source_pw/module_stodft/sto_iter.h

Test code (bulk of usages): test/diago_*_test.cpp, test/diago_mock.h,
test/hsolver_supplementary_mock.h reference structure_factor.h, hamilt_pw.h,
op_pw.h, sto_wf.h.

Notes

The solver should operate against the abstract Hamiltonian interface rather than
concrete PW implementations. Tests likely need mocks/fixtures to avoid pulling in
source_pw, or should be moved to the owning module.

Acceptance criteria

• No #include "source_pw/..." remains in source_hsolver production code.
• Test dependencies on source_pw are removed or replaced with mocks.

Additional Context

No response

Task list for Issue attackers (only for developers)

• 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.