Fix IB data WP_MOK to use stp instead of default integer

The IB read/write displacement formula uses WP_MOK to skip past
floating-point field data. Using storage_size(0) gave the default
integer size (4 bytes), not the field storage precision size, causing
incorrect byte offsets in double-precision builds.

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

Author: sbryngelson

src/post_process/m_data_input.f90

@@ -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(storage_size(0)/8, MPI_OFFSET_KIND)
+                WP_MOK = int(storage_size(0._stp)/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)

src/simulation/m_data_output.fpp

@@ -1087,7 +1087,7 @@ contains
         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(storage_size(0)/8, MPI_OFFSET_KIND)
+        WP_MOK = int(storage_size(0._stp)/8, MPI_OFFSET_KIND)
         MOK = int(1._wp, MPI_OFFSET_KIND)
 
         write (file_loc, '(A)') 'ib.dat'