CVE-2026-86138: add overflow checks to xmlDictAddQString pool size
calculation and bound the QName lengths in its caller xmlDictQLookup to
prevent heap buffer overflow when interning long QNames
CVE-2026-86140: add bounds checks around the englobing parenthesis
strcat() calls in xmlSnprintfElements to prevent stack buffer overflow
CVE-2026-86142: reject XPointer parts whose length is not representable
as an int in xmlXPtrEvalXPtrPart to prevent heap buffer overflow