BIT-libpython-2026-6879: Quadratic Behavior in xml.etree.ElementPath Index Predicates

Element.findall() and fully-consumed Element.iterfind() exhibit O(n^2) time complexity when using XPath index predicates (e.g. [1], [last()], [last()-N]) on XML documents with many same-tag siblings. Element.find() is only affected when the first match is near the end  of the sibling list, such as with [last()] or [last()-N];  .//item[1] short-circuits after the first match.