Terminate all processes on error in parallel_run_from_cli

[yguclu]

Terminate all MPI processes when one of them raises an uncaught exception in psydac.utilities.parallel_utils.parallel_run_from_cli (fixes #621).

Without this, the other processes hang as soon as they wait for a message from the failing one, and a job on a cluster keeps its allocation until it reaches the wall-time limit. The same mechanism as in the launcher python -m mpi4py is used: the exception is passed to mpi4py.run.set_abort_status and re-raised, hence its traceback is printed and the failing process is cleaned up, then MPI_Abort is called at exit. This works with any MPI launcher (e.g. mpirun, mpiexec, or srun in a batch job), and does not require running scripts with python -m mpi4py.

• In parallel_run_from_cli, abort all processes at exit in case of an uncaught exception in main, and document this behavior in the docstring
• Add section "Running examples in parallel" to the Examples page of the documentation (docs/source/examples.rst), which very strongly recommends running every parallel script through parallel_run_from_cli
• New module psydac.utilities.tests.test_parallel_utils, which tests parallel_run_from_cli in serial with and without an exception in main (the call to MPI_Abort is mocked)

The abort was also checked manually with a script failing on one of 4 processes: with the fix, the job terminates with exit code 1 after printing the traceback; without it, the job hangs.

[codacy-production]

Up to standards ✅

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🟢 Metrics 7 complexity · 0 duplication

Metric	Results
Complexity	7
Duplication	0

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🟢 Coverage 100.00% diff coverage · +0.05% coverage variation

Metric	Results
Coverage variation	✅ +0.05% coverage variation
Diff coverage	✅ 100.00% diff coverage

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Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (f2da0cd)	51844	33084	63.81%
Head commit (5943240)	103746 (+51902)	66252 (+33168)	63.86% (+0.05%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#624)	30	30	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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