CVE-2026-86143: reject output buffer lengths that do not fit in an int
before calling writecallback in xmlOutputBufferWrite,
xmlOutputBufferWriteEscape and xmlOutputBufferFlush, so that a negative
length can no longer reach a write callback
CVE-2026-86144: propagate the document parse flags in xmlXIncludeProcess,
xmlXIncludeProcessTree and xmlXIncludeLoadTxt so that options such as
XML_PARSE_NONET are honoured during XInclude resolution