OpenMP Not Working?

[ax3l]

Tested with 1 MPI rank:
It looks like setting OMP_NUM_THREADS to values greater than 1 neither accelerates tracking nor space charge calculations right now. This is a defect.

The init logic shows we use multiple threads, but tracking takes as long with 1 as with 4 threads as of 25.02.

Reproducer (private link):

• https://github.com/ECP-WarpX/impactx-benchmarks/blob/main/spacecharge_impactx.py
• https://github.com/ECP-WarpX/impactx-benchmarks/blob/main/drift_impactx.py
  But any other example (disable diagnostics to reduce noise) shows this as well.