gh-148014: Accept a function name in -X presite option

[vstinner]

• Issue: Accept a function (module_name:function_name) in -X presite and PYTHON_PRESITE #148014

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📚 Documentation preview 📚: https://cpython-previews--148015.org.readthedocs.build/

[vstinner]

"Tests / macOS / build and test (macos-26-intel)" failed but its output is truncated and the UI seems to say that the CI job is still running, whereas it's marked as failed (and not running):

...
0:01:35 load avg: 14.19 [ 97/502] test.test_asyncio.test_locks passed -- running (3): test.test_multiprocessing_spawn.test_processes (31.1 sec), test.test_asyncio.test_tasks (33.4 sec), test_regrtest (30.8 sec)
0:01:36 load avg: 14.19 [ 98/502] test_pty passed -- running (3): test.test_multiprocessing_spawn.test_processes (32.2 sec), test.test_asyncio.test_tasks (34.4 sec), test_regrtest (31.9 sec)

At least, I can re-run the failed job.

[vstinner]

cc @ambv

[warsaw]

I didn't get a chance to look at this before you merged it, but thank you @vstinner ! LGTM and it's a nice addition.