fix(foundation): an abandoned extraction keeps its file open on GraalPy, which never calls __del__ #1997

On GraalPy, an extraction abandoned before EOF (auto=False, stopped early) never releases the file it opened. Extractor.__del__, the #606 backstop that closes it, is never called there.

• Measured on GraalPy 25.4.4: an object's __del__ does not run after del and repeated gc.collect(), either alone or in a cycle. A weakref.finalize on the same object does fire.
• Failing test: test_extraction_ownership.py::ExtractorClosesWhatItOpens::test_extractor_abandoned_before_eof_still_releases_its_handle, on the GraalPy experimental leg (found while working test: sort the remaining GraalPy-only failures into defects and gates #1963 in fix(utilities): leave GraalPy's bootstrap frames out of the importer's level, and gate its remaining limits (#1963) #1996).
• CPython: unaffected.

Possible fix: register the backstop with weakref.finalize on the owned stream instead of, or as well as, __del__. This changes pcapkit/foundation/extraction.py, so it needs a test on both interpreters.