post processing: Adding unit tests

[harriscr]

Add unit tests for the post_processing/* modules, as well as the workloads modules. This will help to make sure that changes in the future to these modules get sufficient testing coverage and mean we can spot issues eariler in the development cycle. The unit tests for CBT have now increased from 348 to 544

An AI code assistant, IBM Bob, was used to help create these unit tests.

The tests all pass:

============================= slowest 5 durations ==============================
0.18s call     tests/test_simple_plotter.py::TestSimplePlotter::test_draw_and_save
0.01s setup    tests/test_bm_cephtestrados.py::TestBenchmarkcephtestrados::test_valid__base_archive_directory
0.01s setup    tests/test_bm_fio.py::TestBenchmarkfio::test_valid__base_archive_directory
0.01s setup    tests/test_bm_getput.py::TestBenchmarkgetput::test_valid__base_archive_directory
0.01s setup    tests/test_bm_radosbench.py::TestBenchmarkradosbench::test_valid__base_archive_directory
================= 544 passed, 3 skipped, 21 warnings in 1.50s ==================
Finished running tests!

There were also some code changes made based on code issues discovered when running the unit tests

[harriscr]

The warnings when running the unit tests all come from the installed version of matplotlib in the python 3.9 virtualenv used:

cbt/ceph.venv/lib64/python3.9/site-packages/matplotlib/_fontconfig_pattern.py:64: DeprecationWarning: 'oneOf' deprecated - use 'one_of'
    prop = Group((name + Suppress("=") + comma_separated(value)) | oneOf(_CONSTANTS))

ceph.venv/lib64/python3.9/site-packages/matplotlib/_fontconfig_pattern.py:85
ceph.venv/lib64/python3.9/site-packages/matplotlib/_fontconfig_pattern.py:85
ceph.venv/lib64/python3.9/site-packages/matplotlib/_fontconfig_pattern.py:85
ceph.venv/lib64/python3.9/site-packages/matplotlib/_fontconfig_pattern.py:85
ceph.venv/lib64/python3.9/site-packages/matplotlib/_fontconfig_pattern.py:85
ceph.venv/lib64/python3.9/site-packages/matplotlib/_fontconfig_pattern.py:85
  /home/harriscr/cbt/ceph.venv/lib64/python3.9/site-packages/matplotlib/_fontconfig_pattern.py:85: DeprecationWarning: 'parseString' deprecated - use 'parse_string'

Running with the latest python 3.14 on my system gives no warnings at all, but we need to keep the python version for CBT in step with that used for Ceph

[harriscr]

Teuthology perf-basic run: https://pulpito.ceph.com/harriscr-2026-01-26_16:05:32-perf-basic-main-distro-default-trial/

I'll do farther runs now I know teuthology is back and update here with them