Fix non-LCAO elecstate energy test mock

[Stardust0831]

Reminder

• I have read AGENTS.md and docs/developers_guide/agent_governance.md.
• This PR is a follow-up to PR Feature: DFT+U for noncollinear spin calculation with PW base #5703; the historical test context is PR Test: Add Unit test for elecstate_energy.cpp #2486.
• I have run focused unit-test verification and listed the results below.
• There are no user-visible or INPUT behavior changes.
• Core-module impact is limited to a test-only replacement and assertions.
• No governance exception is requested.

Linked Issue

No upstream issue linked; this is a follow-up to the non-LCAO test regression introduced by PR #5703.

Unit Tests and/or Case Tests for my changes

• Before the change, building MODULE_ESTATE_elecstate_energy with LCAO disabled failed with an undefined reference to elecstate::ElecState::get_dftu_energy().
• After the change, the same reduced-feature target builds successfully; its CTest entry passes and the test binary reports 13/13 GoogleTest cases passing.
• The LCAO-enabled target also builds; its CTest entry and all 13 GoogleTest cases pass, confirming that the unconditional test replacement does not introduce a duplicate symbol.
• git diff --check passes.
• No full-repository test suite was run; the change is limited to one focused unit-test source.

What's changed?

PR #5703 extended DFT+U to the PW basis and removed the production __LCAO guard around ElecState::get_dftu_energy() and its call from cal_energies(). The unit test added by PR #2486 still defined its lightweight get_dftu_energy() replacement only under __LCAO.

The failure occurs with BUILD_TESTING=ON, ENABLE_MPI=ON, and ENABLE_LCAO=OFF when CMake builds the standalone MODULE_ESTATE_elecstate_energy test executable. That target compiles elecstate_energy.cpp but intentionally does not link the production elecstate_energy_terms.cpp and its DFT+U dependencies. With LCAO disabled, the stale guard removed the test replacement as well, leaving the production call unresolved at link time.

The production ABACUS target is unaffected because the source_estate module compiles both elecstate_energy.cpp and elecstate_energy_terms.cpp.

This PR makes the test replacement available in both LCAO and non-LCAO builds. It also makes both DFT+U assertions expect the replacement's 0.6 contribution, matching the PW DFT+U behavior introduced by #5703. No production source or runtime behavior changes.

Governance Notes

• INPUT/docs changes: none; no INPUT or user-facing behavior changed.
• Core module impact: test-only linkage and expectation maintenance.
• Exceptions requested: none.