Remove MPI dependency, replace with single-process stub for non-MPI builds

- Add mpi_stub.h providing all MPI types/constants/functions as no-ops
  (nprocs=1, myrank=0) with memcpy-based Allreduce and clock_gettime Wtime
- Replace #include <mpi.h> with conditional #ifdef MPI_STUB in 31 files
  (19 headers + 12 source files) preserving ability to build with real MPI
- Change makefile.inc: CLINKER mpiicpx->icpx, add -DMPI_STUB to CXXAPPFLAGS
- Update makefile_and_run.py: run ./ABE directly instead of mpirun -np N
- Set MPI_processes=1 in AMSS_NCKU_Input.py

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

AMSS_NCKU_Input.py

@@ -16,7 +16,7 @@ import numpy
 File_directory   = "GW150914"                    ## output file directory
 Output_directory = "binary_output"               ## binary data file directory
                                                  ## The file directory name should not be too long
-MPI_processes    = 64                             ## number of mpi processes used in the simulation
+MPI_processes    = 1                              ## number of processes (MPI removed, single-process mode)
 
 GPU_Calculation  = "no"                          ## Use GPU or not 
                                                  ## (prefer "no" in the current version, because the GPU part may have bugs when integrated in this Python interface)