Handle CalledProcessError better

[heplesser]

This PR makes sure that CalledProcessError occurring during MPI testing are caught and reported more clearly. High up in the output one will now get a report like this:

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Running failed for: ['mpirun', '-np', '1', '--oversubscribe', 'python', 'runner.py']
tmpdir            : /var/folders/zz/kr57pbys6f5dtt17dk7jjh4c0000gn/T/tmprff6aso7
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STDOUT
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              -- N E S T --
  Copyright (C) 2004 The NEST Initiative

 Version: 3.8.0-post0.dev0
 Built: Mar 17 2025 22:55:56

 This program is provided AS IS and comes with
 NO WARRANTY. See the file LICENSE for details.

 Problems or suggestions?
   Visit https://www.nest-simulator.org

 Type 'nest.help()' to find out more about NEST.


--------------------------------------------------
STDERR
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Traceback (most recent call last):
  File "/private/var/folders/zz/kr57pbys6f5dtt17dk7jjh4c0000gn/T/tmprff6aso7/runner.py", line 22, in <module>
    test_all_to_all(N=7)
  File "/private/var/folders/zz/kr57pbys6f5dtt17dk7jjh4c0000gn/T/tmprff6aso7/runner.py", line 17, in test_all_to_all
    nest.Connect(nrns, nrns, 'all_to_all2')
  File "/Users/plesser/NEST/code/bld/main/mpi/install/lib/python3.12/site-packages/nest/ll_api.py", line 216, in stack_checker_func
    return f(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^
  File "/Users/plesser/NEST/code/bld/main/mpi/install/lib/python3.12/site-packages/nest/lib/hl_api_connections.py", line 289, in Connect
    sr("Connect")
  File "/Users/plesser/NEST/code/bld/main/mpi/install/lib/python3.12/site-packages/nest/ll_api.py", line 103, in catching_sli_run
    raise exceptionCls(commandname, message)
nest.lib.hl_api_exceptions.NESTErrors.BadProperty: BadProperty in SLI function Connect_g_g_D_D: Unknown connection rule: all_to_all2

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[JanVogelsang]

Neat!

[heplesser]

@JanVogelsang I have now extended this PR so that it (a) returns empty dataframes/json strings if no connections are present in keeping with the requested data type and (b) data collection for "OTHER" works correctly if a rank does not deliver data (empty file).

[heplesser]

Minor test setup improvement, merging based on single review.