Fix WP_MOK hardcoded to 8 bytes, use storage_size for precision portability

MPI file offsets assume 8-byte reals. Single-precision builds would
read from wrong offsets. Use storage_size(0._wp)/8 instead.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sbryngelson

src/post_process/m_data_input.f90

@@ -133,7 +133,7 @@ impure subroutine s_setup_mpi_io_params(data_size, m_MOK, n_MOK, p_MOK, WP_MOK,
         m_MOK = int(m_glb + 1, MPI_OFFSET_KIND)
         n_MOK = int(n_glb + 1, MPI_OFFSET_KIND)
         p_MOK = int(p_glb + 1, MPI_OFFSET_KIND)
-        WP_MOK = int(8._wp, MPI_OFFSET_KIND)
+        WP_MOK = int(storage_size(0._wp)/8, MPI_OFFSET_KIND)
         MOK = int(1._wp, MPI_OFFSET_KIND)
         str_MOK = int(name_len, MPI_OFFSET_KIND)
         NVARS_MOK = int(sys_size, MPI_OFFSET_KIND)
@@ -177,7 +177,7 @@ impure subroutine s_read_ib_data_files(file_loc_base, t_step)
                 n_MOK = int(n_glb + 1, MPI_OFFSET_KIND)
                 p_MOK = int(p_glb + 1, MPI_OFFSET_KIND)
                 MOK = int(1._wp, MPI_OFFSET_KIND)
-                WP_MOK = int(8._wp, MPI_OFFSET_KIND)
+                WP_MOK = int(storage_size(0._wp)/8, MPI_OFFSET_KIND)
                 save_index = t_step/t_step_save ! get the number of saves done to this point
 
                 data_size = (m + 1)*(n + 1)*(p + 1)
@@ -517,7 +517,7 @@ impure subroutine s_read_parallel_conservative_data(t_step, m_MOK, n_MOK, p_MOK,
                 m_MOK = int(m_glb + 1, MPI_OFFSET_KIND)
                 n_MOK = int(n_glb + 1, MPI_OFFSET_KIND)
                 p_MOK = int(p_glb + 1, MPI_OFFSET_KIND)
-                WP_MOK = int(8._wp, MPI_OFFSET_KIND)
+                WP_MOK = int(storage_size(0._wp)/8, MPI_OFFSET_KIND)
                 MOK = int(1._wp, MPI_OFFSET_KIND)
                 str_MOK = int(name_len, MPI_OFFSET_KIND)
                 NVARS_MOK = int(sys_size, MPI_OFFSET_KIND)