Refactor DFT+U: rename and de-static Plus_U members, step 3 - #7859

… force and stress

Seven members (yukawa_lambda, npol, nlocal, gamma_only_local, ks_solver, cal_force, cal_stress) were only read by the LCAO subclass (Plus_U) and its component files under source_lcao/module_dftu/. They are now declared in Plus_U and assigned in Plus_U::init, so Plus_U_Base no longer carries LCAO-specific mutable workflow state.

Accordingly shorten Plus_U_Base::init_base signature by six parameters (yukawa_lambda, nlocal, gamma_only_local, ks_solver, cal_force, cal_stress); update the two call sites (Plus_U::init in dftu.cpp, PW path in setup_pot.cpp). Plus_U::init keeps its original signature so external callers (lcao_set.cpp) are unaffected.

dftu.hpp only provided the empty primary template for hamilt::DFTU. Move it into dftu_lcao.h (the sole includer), guarded by __DFTUTEMPLATE, matching the convention used by sibling LCAO operators (nonlocal.h, ekinetic.h, meta_lcao.h, veff_lcao.h, etc.) that inline the primary template instead of using a separate .hpp file. This also aligns with AGENTS.md rule 4 (avoid .hpp implementation headers).

Three LCAO DFT+U files had confusing names that hid which was the main implementation, the new operator, and the legacy operator. Rename for clarity:

  - dftu.h/.cpp -> dftu_lcao.h/.cpp   : Plus_U class (LCAO DFT+U physics, subclass of Plus_U_Base in dftu_base.h). The name now mirrors dftu_base.h.

  - dftu_lcao.h/.cpp -> dftu_lcao_op.h/.cpp : hamilt::DFTU operator (new method, dft_plus_u==1, onsite_radius projections). Operators now carry the _op suffix.

  - op_dftu_lcao.h/.cpp -> dftu_lcao_op_legacy.h/.cpp : hamilt::OperatorDFTU operator (old method, dft_plus_u==2, NAO first zeta projections, test-only). Renamed to mark it as legacy and group it with the new operator.

Class names are unchanged in this step (Plus_U, hamilt::DFTU, hamilt::OperatorDFTU); only filenames and #include paths change. Updated all ~40 includers across source_lcao, source_pw, source_esolver, source_estate, source_io, plus the module and test CMakeLists (the dftu_lcao_test links the new-operator cpp ../dftu_lcao_op.cpp, not the Plus_U cpp).

…yers

Replace Plus_U (LCAO-derived class) with Plus_U_Base (PW-layer base class) in
all non-LCAO interfaces. All DFT+U calls in PW/estate/test layers only use
base-class members, so the derived-type reference was unnecessary.

Changes:
- Remove #include "source_lcao/module_dftu/dftu_lcao.h" from PW/base headers
- Use #include "source_pw/module_pwdft/dftu_base.h" instead
- Replace Plus_U&/Plus_U* with Plus_U_Base&/Plus_U_Base* in:
  * source_pw/module_pwdft: force_pw, hamilt_pw, onsite_proj, op_pw_proj,
    stress_func, stress_onsite, stress_pw (6 headers + 7 impls)
  * source_estate/module_charge: chgmixing (PW + LCAO mixing functions)
  * source_pw/module_stodft/test: test_hamilt_sto, test_sto_tool
  * source_hsolver/test: diago_mock.h (3 explicit specializations)

Plus_U (derived) instances held by callers (e.g. ESolver_KS::dftu) continue
to work via implicit pointer/reference upcast to Plus_U_Base. No behavioral
change.