Add BSD support for track-memory

[lcheylus]

• Add BSD bool variable (= true if running on BSD OS)
• Use psutil to get memory infos on BSD
• Use psutil.memory_info().rss on BSD instead of memory_full_info().uss (not supported)

Fix #219

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Tests OK on OpenBSD current/amd64 with Python 3.12.11

$ pytest
============================= test session starts =============================
platform openbsd7 -- Python 3.12.11, pytest-8.4.2, pluggy-1.6.0
rootdir: /home/fox/dev/pyperf.git
configfile: pyproject.toml
collected 173 items

pyperf/tests/test_bench.py ...................................          [ 20%]
pyperf/tests/test_cli.py ..                                             [ 21%]
pyperf/tests/test_examples.py ........                                  [ 26%]
pyperf/tests/test_metadata.py .....                                     [ 28%]
pyperf/tests/test_misc.py .........                                     [ 34%]
pyperf/tests/test_perf_cli.py ...................................       [ 54%]
pyperf/tests/test_runner.py .............................               [ 71%]
pyperf/tests/test_system.py .                                           [ 71%]
pyperf/tests/test_timeit.py ...............................             [ 89%]
pyperf/tests/test_utils.py ..................                           [100%]

============================ 173 passed in 47.13s =============================

[vstinner]

Can you add a comment to explain this change?

[vstinner]

It would be better to do something like:

elif LINUX:
    from pyperf._linux_memory import check_tracking_memory
else:
    from pyperf._psutil_memory import check_tracking_memory

Same remark for MemoryUsage below.