refactor(stodft): replace new[]/delete[] with std::vector in info_gatherv

[xinchenhou]

What this PR does

Replace raw new[]/delete[] with std::vector in source/source_pw/module_stodft/sto_tool.h.

Why

• std::vector manages memory automatically, removing the need for manual delete[].
• This follows the ABACUS governance rule: "Prefer std::vector over raw new/delete for dynamic arrays".

Changes

• info_gatherv::nrecv and info_gatherv::displs changed from int* to std::vector<int>.
• Constructor initializes vectors in the member initializer list.
• Destructor removed; std::vector handles cleanup.
• MPI_Allgather now receives nrecv.data() instead of raw pointer.
• Added #include <vector> to sto_tool.h because std::vector<int> is now a member type of info_gatherv and member variables require complete types (forward declaration is not possible for template classes).
• Updated call sites in source/source_pw/module_stodft/sto_elecond.cpp to pass nrecv.data() / displs.data() to the existing int* interfaces (gatherchi_op, Parallel_Common::gatherv_data).

Note on file count: The original task description mentioned modifying only one file, but sto_elecond.cpp consumes info_gatherv::nrecv/displs as raw int*. After the change to std::vector<int>, those call sites require .data() to compile. Hence two files are modified, but the diff remains under 20 lines.

Verification performed

• Build: cmake --build build -j 8 (with ENABLE_LCAO=OFF, ENABLE_ELPA=OFF due to local environment constraints)
• Unit test: ctest --test-dir build -R MODULE_PW_Sto -V
  • Result: 100% tests passed, 0 tests failed out of 3
  • MODULE_PW_Sto_Tool_UTs PASSED (covers sto_tool.h)
  • MODULE_PW_Sto_Hamilt_UTs PASSED
  • MODULE_PW_Sto_HSolver_UTs PASSED
• Governance check: python3 tools/03_code_analysis/agent_governance_check.py --staged
  • Result: 3 warnings, 0 errors
  • Warning 1 (header include): Justified — std::vector<int> is a member type and requires complete type, cannot forward declare
  • Warning 2 (no test changes): Justified — pure refactor with no behavior change, existing tests already cover the modified code
  • Warning 3 (no docs changes): Justified — internal implementation detail, no public API or user-facing behavior change

Documentation

No documentation update needed. This change is internal to info_gatherv and does not affect any public API, user-facing behavior, or input parameters.

Checklist

• No new #define private public in tests
• No new .hpp implementation headers
• No default arguments added to existing interfaces
• C++11 compatible (uses std::vector::data() which is C++11)
• One variable per line declared

[ABACUS-PR-BOT]

Static review of b9acd92: no correctness regression identified in the ownership conversion or caller updates. No builds or runtime tests were run; CI retrieval was unavailable.