Fix stale module names in example/pbs/config_mpi.ini

The MPI example config still used the pre-suffix module names
(`python_example`, `serial_example`, `execute_example`) and section
headers from 2019-2020; the module loader needs the full runner names
(`*_runner`), as example/config.ini uses. With the stale names, rank 0
failed with "No module named 'shapepipe.modules.python_example'" and the
other ranks deadlocked in the collective until the wall-clock timeout.

Third layer of MPI bit-rot beneath the launcher and the module_config_sec
fix, same root cause: nobody runs MPI, so its example config rotted too.

Verified: the unmodified candide_mpi.sh against the published runtime image
now runs the example pipeline end-to-end (4 ranks / 2 nodes, all three
modules, 0 errors, exit 0).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: cailmdaley

example/pbs/config_mpi.ini

@@ -2,7 +2,7 @@
 
 ## ShapePipe execution options
 [EXECUTION]
-MODULE = python_example, serial_example, execute_example
+MODULE = python_example_runner, serial_example_runner, execute_example_runner
 MODE = mpi
 
 ## ShapePipe file handling options
@@ -15,8 +15,8 @@ OUTPUT_DIR = $SPDIR/example/output
 TIMEOUT = 00:01:35
 
 ## Module options
-[PYTHON_EXAMPLE]
+[PYTHON_EXAMPLE_RUNNER]
 MESSAGE = The obtained value is:
 
-[SERIAL_EXAMPLE]
+[SERIAL_EXAMPLE_RUNNER]
 ADD_INPUT_DIR = $SPDIR/example/data/numbers, $SPDIR/example/data/letters