Fix: Fix ELF for kpar > 1

[sunliang98]

Reminder

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• Have you added adequate unit tests and/or case tests for your pull request?
• Have you noticed possible changes of behavior below or in the linked issue?
• Have you explained the changes of codes in core modules of ESolver, HSolver, ElecState, Hamilt, Operator or Psi? (ignore if not applicable)

Linked Issue

Fix #7305

Unit Tests and/or Case Tests for my changes

What's changed?

Problem
When running with kpar > 1, ELF output was incorrect. The root cause was that cal_tau() called rho_mpi() again, which re‑reduced rho across k‑point pools and effectively scaled the density by kpar. Since tau_vw depends on $|\nabla \sqrt{\rho}|^2$, this led to incorrect ELF.

Fix
Added Charge::kin_r_mpi() to reduce only kin_r across kpar/bndpar, and updated ElecStatePW::cal_tau() to call this new function. This avoids re‑reducing rho while keeping kin_r properly reduced.

Validation
ELF outputs computed with the updated code are consistent for kpar=1/4.

Any changes of core modules? (ignore if not applicable)

• Example: I have added a new virtual function in the esolver base class in order to ...

[Copilot]

Pull request overview

Fixes incorrect ELF output when running with kpar > 1 by preventing an unintended second reduction of rho during tau/ELF preparation, and instead reducing only kin_r across k-point/band pools.

Changes:

• Added Charge::kin_r_mpi() to MPI-reduce only kin_r across k-point/band parallel pools.
• Updated ElecStatePW::cal_tau() to call kin_r_mpi() instead of the broader parallelK()/rho_mpi() path.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
source/source_estate/module_charge/charge_mpi.cpp	Adds Charge::kin_r_mpi() to reduce only kinetic energy density (kin_r) across pools.
source/source_estate/module_charge/charge.h	Declares the new kin_r_mpi() API on Charge.
source/source_estate/elecstate_pw_cal_tau.cpp	Switches cal_tau() to reduce only kin_r, avoiding re-reducing rho.

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