test(qualification): handle process exit during procfs status reads

[DivyamTalwar]

Root cause

Fixes #59. PR #58's Linux/Python 3.11 run reproduced an observation race in the pre-existing test helper: /proc/<pid>/stat disappeared after the existence check, raising ProcessLookupError while checking an already-exited owned child.

Change

• Treat FileNotFoundError and ProcessLookupError during that status read as process disappearance.
• Preserve permission and malformed-record errors instead of calling an unknown observation a dead process.
• Parse the status after the process-name closing parenthesis, so spaces in a process name do not hide zombie state.
• Keep the real process-group cleanup, timeout/output-limit and unrelated-child survival assertions unchanged.
• Add seven deterministic disappearance, live/zombie, permission and malformed-data controls.

This changes test observation only. It does not alter product subprocess cleanup or loosen its assertions.

Verification

Candidate 75821f2d6c5e717400c83377c11035e13f9a5899, based on PR #49.

PYTHONPATH=$PWD python -m pytest -q -p no:cacheprovider
# 889 passed, 0 failed, 0 skipped; 3 expected optional-provider warnings
python -m compileall -q jitmind tests
python -m pip check
git diff --check
# passed

The supervisor verified unchanged source hashes during the run. The Linux race itself is evidenced by run https://github.com/DivyamTalwar/JITMIND/actions/runs/36506320213; the local macOS run uses deterministic procfs observations plus the unchanged real child-process tests. It is not relabelled as a native Linux reproduction.

Stacked on #49. This small follow-up will precede #58 so the instrumentation PR can retain a focused diff and rerun its complete matrix. No automatic merge.