zip_header.nx

zip_header.nx -- parse PKZIP APPNOTE 6.3.x framing. Parses two key structures in a .zip archive: 1. Local File Header (LFH) -- one per stored file, prefixes each compressed payload. Signature 0x04034b50. 2. End of Central Directory record (EOCD) -- at the tail of the archive; points to the central directory. Signature 0x06054b50. This module does NOT parse the central directory entries (CDFH) or decompress payloads. With just LFH + EOCD the Nishi stack can: detect zip framing, count members, read filenames, identify compression method (0=stored, 8=DEFLATE, 14=LZMA, 93=Zstd...), and find the offset of each file's raw bytes. All multi-byte values in ZIP are little-endian. Invariants: Z1 LFH signature must be 0x04034b50. Z2 EOCD signature must be 0x06054b50 (may be preceded by a variable-length ZIP comment; caller scans backward). Z3 Filenames are stored raw; if bit 11 of general-purpose flag is set, they are UTF-8; otherwise CP437. We expose offset+length and let caller decide. Z4 Compressed-size / uncompressed-size may be 0xFFFFFFFF to indicate Zip64 extensions; we surface that as a sentinel for now.