Lower coverage under Spark

[luiztauffer]

Function calls that are distributed through Spark workers do net get automatically included in the coverage report, even though they are running and successfully passing the tests, e.g.:

---------- coverage: platform linux, python 3.12.4-final-0 -----------
Name                                      Stmts   Miss  Cover   Missing
-----------------------------------------------------------------------
voluseg/__init__.py                          10      0   100%
voluseg/_steps/__init__.py                    0      0   100%
voluseg/_steps/step0.py                     124     41    67%   20, 25, 34-35, 50, 56, 62, 78, 84, 86, 92, 94, 100-104, 111, 115, 122-128, 146-161, 178, 187, 193-204, 231-232
voluseg/_steps/step1.py                      71     53    25%   19, 26-122
voluseg/_steps/step2.py                      87     50    43%   6, 27, 36, 42, 47-53, 56-144
voluseg/_steps/step3.py                     177     31    82%   48-60, 69, 75-78, 93, 130, 138-143, 148-149, 177-183
voluseg/_steps/step4.py                     114     51    55%   36, 47-52, 75, 100-103, 113-227
voluseg/_steps/step4a.py                     42      2    95%   22-23
voluseg/_steps/step4b.py                     62     61     2%   15-102
voluseg/_steps/step4c.py                     40     39     2%   17-84
voluseg/_steps/step4d.py                     56     55     2%   23-105
voluseg/_steps/step4e.py                     64     27    58%   40-65, 71-79
voluseg/_steps/step5.py                     121     13    89%   28, 47-48, 57-58, 98-99, 105-107, 158, 165-166
voluseg/_tools/__init__.py                    1      0   100%
voluseg/_tools/ants_registration.py           7      6    14%   13-61
voluseg/_tools/ants_transformation.py         4      3    25%   6-26
voluseg/_tools/ball.py                       11      0   100%
voluseg/_tools/clean_signal.py               43      5    88%   28-29, 61-63
voluseg/_tools/constants.py                   5      0   100%
voluseg/_tools/evenly_parallelize.py          9      0   100%
voluseg/_tools/get_volume_name.py             8      2    75%   10, 14
voluseg/_tools/load_metadata.py              26     25     4%   4-41
voluseg/_tools/load_parameters.py             9      2    78%   13-14
voluseg/_tools/load_volume.py                38     12    68%   23-31, 36-37, 41
voluseg/_tools/parameter_dictionary.py        2      0   100%
voluseg/_tools/sample_data.py                27     21    22%   24-55
voluseg/_tools/save_volume.py                19     18     5%   4-26
voluseg/_tools/sparseness.py                  6      6     0%   1-9
voluseg/_tools/sparseness_projection.py      29     29     0%   1-57
voluseg/_update.py                            3      2    33%   4-6
-----------------------------------------------------------------------
TOTAL                                      1215    554    54%

some references:

• https://coverage.readthedocs.io/en/latest/subprocess.html
• https://stackoverflow.com/questions/60736080/python-coverage-subprocess-coverage-process-startup-error
• Coverage of pyspark user defined function nedbat/coveragepy#658
• https://stackoverflow.com/questions/67167957/getting-coverage-xml-for-a-python-file-run-with-spark/67184714#67184714