Balance the EXX q-pack timer when output is disabled

[Critsium-xy]

Reminder

• I have read AGENTS.md and docs/developers_guide/agent_governance.md.
• I have linked an issue or explained why this PR does not need one.
• I have added adequate unit tests and/or case tests, or explained why not.
• I have listed the exact verification commands run and their results.
• I have described user-visible behavior changes, including INPUT parameter changes.
• I have explained core-module impact for ESolver, HSolver, ElecState, Hamilt, Operator, Psi, or other source/ changes.
• I have requested any needed governance exception below.

Linked Issue

Fix #7545

Unit Tests and/or Case Tests for my changes

• Commands run:
  • cmake -S . -B /tmp/abacus-build-mpi-openblas
  • cmake --build /tmp/abacus-build-mpi-openblas --target abacus_basic_para -j2
  • cmake --build /tmp/abacus-build-mpi-openblas --target MODULE_BASE_timer -j2
  • OMP_NUM_THREADS=1 ctest --test-dir /tmp/abacus-build-mpi-openblas --output-on-failure -R ^MODULE_BASE_timer$
  • git diff --check
  • python3 tools/03_code_analysis/agent_governance_check.py --staged
  • python3 tools/03_code_analysis/agent_governance_check.py --base upstream/develop --head HEAD --format text
• Result summary: the LCAO-enabled abacus_basic_para target completed all 555 build steps; MODULE_BASE_timer passed; diff checks passed. Governance emitted test-evidence and documentation reminders addressed below.
• Environment note: MPI-linked compilation printed the documented sandbox artifact opal_ifinit: socket() failed errno=1, but every compile and link step completed successfully.
• Earlier command correction: the first build command used the nonexistent generic target abacus; the configured executable target is abacus_basic_para, which subsequently built successfully.
• Checks not run, with reason: no dedicated Exx_Lip::write_q_pack runtime test was added because the template has no lightweight independently constructible fixture and its constructor requires the full LCAO/PW electronic-state stack. The full owning executable build instantiates the changed template, and the timer component test covers timer start/end invariants.

What changed?

• Return before starting the write_q_pack timer when charge output is disabled.
• Preserve the existing paired timer start/end calls on the enabled-output path.

Governance Notes

• INPUT/docs changes: no INPUT semantics or output contents changed; only internal timing statistics are corrected, so user documentation is not required.
• Core module impact: limited to the legacy EXX LIP output helper; numerical EXX calculations and q-pack output are unchanged.
• Global dependency budget: the existing PARAM check was moved before the timer start; no global references were added.
• Existing .hpp rationale: this PR modifies an existing template implementation header and does not add or propagate a new .hpp include.
• Exceptions requested: none.