gh-150114: Use get_process_memory_usage() in memory watchdog

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In practice, this change adds Windows and FreeBSD support to the memory watchdog.

• Issue: GitHub free threading CI failing with SIGTERM #150114

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Example on Linux:

$ ./python -m test test_bigmem -u all -M 20G -v
== CPython 3.16.0a0 (tags/v3.15.0b1-20-g57ef2199503:57ef2199503, May 25 2026, 15:08:14) [GCC 16.1.1 20260515 (Red Hat 16.1.1-2)]
== Linux-7.0.9-204.fc44.x86_64-x86_64-with-glibc2.43 little-endian
== Python build: debug TraceRefs
== cwd: /home/vstinner/python/main/build/test_python_worker_308892æ
== CPU count: 12
== encodings: locale=UTF-8 FS=utf-8
== resources: all
Using random seed: 1234531347
0:00:00 load avg: 1.57 mem: 28.3 MiB Run 1 test sequentially in a single process
0:00:00 load avg: 1.57 mem: 28.3 MiB [1/1] test_bigmem
test_capitalize (test.test_bigmem.BytearrayTest.test_capitalize) ... ... expected peak memory use: 4.0 GiB
... process data size: 0.5 GiB
... process data size: 2.4 GiB
... process data size: 4.0 GiB
... process data size: 4.0 GiB
... process data size: 4.0 GiB
(...)

cc @cmaloney

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In practice, this change adds Windows and FreeBSD support to the memory watchdog.

macOS support is coming: see PR gh-150396.

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"Tests / Windows (free-threading) / Build and test (x64, switch-case)" failed with:

FAIL: test_generator_not_under_consumer_arithmetic (test.test_profiling.test_sampling_profiler.test_blocking.TestBlockingModeStackAccuracy.test_generator_not_under_consumer_arithmetic)
Test that fibonacci_generator doesn't appear when consume_generator does arithmetic.
----------------------------------------------------------------------
Traceback (most recent call last):
File "D:\a\cpython\cpython\Lib\test\test_profiling\test_sampling_profiler\test_blocking.py", line 137, in test_generator_not_under_consumer_arithmetic
self.assertEqual(invalid_stacks, 0,
~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
f"Found {invalid_stacks}/{arithmetic_samples} invalid stacks where "
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
f"fibonacci_generator appears in the stack when consume_generator "
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
f"is on an arithmetic line. This indicates torn/inconsistent stack "
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
f"traces are being captured.")
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 639 != 0 : Found 639/4508 invalid stacks where fibonacci_generator appears in the stack when consume_generator is on an arithmetic line. This indicates torn/inconsistent stack traces are being captured.
======================================================================
ERROR: test_getwche (test.test_msvcrt.TestConsoleIO.test_getwche)
----------------------------------------------------------------------
Traceback (most recent call last):
File "D:\a\cpython\cpython\Lib\test\test_msvcrt.py", line 102, in test_getwche
self.check_getwch('getwche')
~~~~~~~~~~~~~~~~~^^^^^^^^^^^
File "D:\a\cpython\cpython\Lib\test\test_msvcrt.py", line 92, in check_getwch
self.run_in_separated_process(code)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
File "D:\a\cpython\cpython\Lib\test\test_msvcrt.py", line 70, in run_in_separated_process
subprocess.run(cmd, check=True, capture_output=True,
~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
creationflags=subprocess.CREATE_NEW_CONSOLE)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "D:\a\cpython\cpython\Lib\subprocess.py", line 692, in run
raise CalledProcessError(retcode, process.args,
output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['D:\\a\\cpython\\cpython\\PCbuild\\amd64t\\python_d.exe', '-c', '\nimport msvcrt\nfrom _testconsole import write_input\nwith open("CONIN$", "rb", buffering=0) as stdin:\n write_input(stdin, b\'W[\')\n assert msvcrt.getwche() == "å­—"\n']' returned non-zero exit status 3221225794.
======================================================================
FAIL: test_python_legacy_windows_stdio (test.test_cmd_line.CmdLineTest.test_python_legacy_windows_stdio)
----------------------------------------------------------------------
Traceback (most recent call last):
File "D:\a\cpython\cpython\Lib\test\test_cmd_line.py", line 1047, in test_python_legacy_windows_stdio
self.assertEqual(p.returncode, 0)
~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
AssertionError: 3221225794 != 0

3221225794 is 0xc0000142 (STATUS_DLL_INIT_FAILED) error code.

I restarted the job.

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@cmaloney: I updated my PR. Thanks for the review. Please review the updated PR.

[cmaloney]

Nice improvement overall; I don't have a BSD system to test. Definitely an improvement on macOS.

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FAIL: test_python_legacy_windows_stdio (test.test_cmd_line.CmdLineTest.test_python_legacy_windows_stdio)
----------------------------------------------------------------------
Traceback (most recent call last):
File "D:\a\cpython\cpython\Lib\test\test_cmd_line.py", line 1047, in test_python_legacy_windows_stdio
self.assertEqual(p.returncode, 0)
~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
AssertionError: 3221225794 != 0

I created issue gh-150436 to track this issue.