File-Per-Process IB markers

[danieljvickers]

For some reason, I never added file-per-process for IB markers, and it is a slowdown constaint for some of the IB cases we are running. Adding this here. I tested this on the 2D_mibm_shock_cylinder case on 2 ranks and verified the visual output was correct.

Even though this is marked as "draft", it is ready for merge.

[github-actions]

Lines of Code

File	Lines	Diff
src/simulation/m_data_output.fpp	1333	+16
src/post_process/m_data_input.f90	420	+12

Directory	Lines	Diff
simulation	28028	+16
post_process	3349	+12
total	45677	+28

[github-actions]

Claude Code Review

Head SHA: f0f2b3c

Files changed:

• 2
• src/post_process/m_data_input.f90
• src/simulation/m_data_output.fpp

Findings:

• src/post_process/m_data_input.f90:119-127: t_step_string is declared only inside the #ifdef MFC_MPI block (lines 114-120), but the new parallel_io .and. file_per_process branch that references it (call s_int_to_str(t_step, t_step_string) and the subsequent write/concatenation) sits outside any #ifdef MFC_MPI guard. In a non-MPI build this branch still has to compile (Fortran doesn't skip unreached branches), so t_step_string is an undeclared identifier there and the file fails to compile without MFC_MPI defined, breaking the CPU/non-MPI build path.