fix(klist): restore nkstot loop bound in pack_kpts to fix heap overflow

bee21a3 changed the kvec_c_full loop in pack_kpts from `nkstot` to
`kvec_c_full.size()`, but the aux buffer is still allocated as
`nkstot_nospin * 3` (which equals `nkstot * 3` at the assignment point
in klist.cpp:291, before spin doubling).

For nspin=2 cases (spin_mult=2), kvec_c_full has been resized to
`nkstot * 2` by renew(), so the new loop writes 2x past the end of
kvec_c_full_aux, corrupting the heap and causing `free(): invalid
pointer` when ESolver_FP is destroyed.

Restore the original `nkstot` bound so the behavior matches the
pre-refactor code exactly. The aux buffer (allocated as
`nkstot_nospin * 3`) and bcast length (`nkstot_nospin * 3`) are
unchanged; only the loop upper bound is restored.

Verified: 12 failed 01_PW tests (003, 007, 028, 030, 034, 036, 037,
050, 055, 063, 078, 079, 097x2, 206, 815, scf_deltaspin2) all pass
again; valgrind reports no Invalid write from ABACUS code.

Author: abacus_fixer

source/source_cell/klist_io.cpp

@@ -273,10 +273,6 @@ void pack_kpts(const std::vector<int>& isk,
         kvec_d_aux[3 * ik] = kvec_d[ik].x;
         kvec_d_aux[3 * ik + 1] = kvec_d[ik].y;
         kvec_d_aux[3 * ik + 2] = kvec_d[ik].z;
-    }
-    const int nkstot_full = static_cast<int>(kvec_c_full.size());
-    for (int ik = 0; ik < nkstot_full; ik++)
-    {
         kvec_c_full_aux[3 * ik] = kvec_c_full[ik].x;
         kvec_c_full_aux[3 * ik + 1] = kvec_c_full[ik].y;
         kvec_c_full_aux[3 * ik + 2] = kvec_c_full[ik].z;