GHSA-VP2X-QP44-57V7 NLTK: Quadratic CPU Exhaustion in `XMLCorpusView._read_xml_fragment()`

Summary XMLCorpusView.readxmlfragment reads a corpus file in 1 KiB blocks, appending each block to a growing fragment string, then calls VALIDXMLRE.matchfragment on the full accumulated buffer every iteration. Because each iteration rescans the entire accumulated fragment, the total amount of wor...