Pull request #1990: PIPE-3262
Merge in PIPE/pipeline from PIPE-3262 to main
* commit '8d3c214a77b5638e53eed418fafc0f126617e138': PIPE-3262: prevent MPI import deadlock and drop `casaplotserver` in pixi PIPE-3262: avoid unconditional mpi4py import in `daskhelpers.py`
PIPE-3262: prevent MPI import deadlock and drop `casaplotserver` in pixi
- Add dynamic `scripts/stubs/casalith.py` to defer MPI initialization to casashell script scope and avoid casatasks import-lock deadlocks (CAS-14037).
- Propagate PYTHONPATH with scripts/stubs in pixi `casa` and `casampi` tasks.
- Remove unused `casaplotserver` dependency from `pyproject.toml` and lockfile.
PIPE-3262: avoid unconditional mpi4py import in `daskhelpers.py`
Use `MPIEnvironment.mpi_processor_rank` instead of `mpi4py.MPI.COMM_WORLD.Get_rank()` to prevent unmanaged `MPI_Init` calls and potentially crashes in macOS serial sessions environments with OpenMPI build/version mismatches.
