fix(Makefile): add missing klist_io.o to OBJS_CELL

The this-free helpers extracted into source_cell/klist_io.cpp are
referenced by klist.cpp, but the Makefile object list was not updated
when the CMake build gained the new TU, breaking the Makefile link with
undefined references to KListIO::ibz_kpt_table/ibz_wk_table/interp_line.

Author: abacus_fixer

source/Makefile.Objects

@@ -211,6 +211,7 @@ OBJS_CELL=atom_pseudo.o\
     print_cell.o\
     setup_nonlocal.o\
     klist.o\
+    klist_io.o\
     reciprocal_grid.o\
     cell_index.o\
     cell_tools.o\