gh-151496: Use process groups in TraceBackend in test_dtrace

[stratakis]

Run the generic DTrace/SystemTap commands in a new process group and terminate the whole group on timeout.

This prevents a forked tracer child from keeping stdout/stderr pipes open after the direct tracer process is killed.

Followup to #151512

• Issue: test_dtrace can hang indefinitely when bpftrace usability check times out #151496

[stratakis]

cc @vstinner

[vstinner]

The two CI failures are unrelated to the change. Let me re-run failed jobs.

Tests / Sanitizers / TSan (free-threading) (pull_request): Failing after 33m

test_abc timed out: that's issue gh-151593.

Tests / macOS (free-threading) / build and test (macos-26) (pull_request): Failing after 9m

It's the first time that I see this failure:

FAIL: test_tk_caret (test.test_tkinter.test_misc.MiscTest.test_tk_caret)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/runner/work/cpython/cpython/Lib/test/test_tkinter/test_misc.py", line 487, in test_tk_caret
    self.assertEqual(caret, {'x': 5, 'y': 10, 'height': 20})
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: {'height': 0, 'x': 0, 'y': 0} != {'x': 5, 'y': 10, 'height': 20}
- {'height': 0, 'x': 0, 'y': 0}
?                    ^

+ {'height': 20, 'x': 5, 'y': 10}
?            +        ^       +

[vstinner]

LGTM. Thanks for the fix.

[miss-islington-app]

Thanks @stratakis for the PR, and @vstinner for merging it 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖

[bedevere-app]

GH-152082 is a backport of this pull request to the 3.15 branch.