CVE-2026-7210: seed Expat's hash-flooding protection with a full 16 bytes
(128 bits) of entropy via XML_SetHashSalt16Bytes() when the loaded libexpat
provides it (detected via a weak symbol), instead of the brute-forceable
8-byte XML_SetHashSalt(); the pyexpat CAPI gains a SetHashSalt16Bytes
pointer appended at the end of the struct (capsule magic unchanged) and
_Py_HashSecret_t gains a 16-byte hashsalt16 field. Both call sites fall back
to the legacy 8-byte API when the salt is all zeros (hash randomization off,
the default) so Expat keeps self-seeding. Paired with the libexpat
CVE-2026-41080 backport that exports the symbol; requires
expat >= 2.1.0-15.0.7.el7_9.tuxcare.els3, the release shipping it