4x-reg-sax-fixes

[tballison]

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[utafrali]

The overall direction is correct: these changes make Tika more resilient against truncated and malformed OOXML/ZIP files by converting hard failures into metadata warnings. The main blocker is a real NPE bug in the OPCPackageDetector fallback path where a missing [Content_Types].xml entry would silently crash rather than be caught by the IOException handler. The other issues (FQCN style, continue after iterator failure, no tests) are smaller but worth addressing before merge.