Use bit-level addressing for xorb chunk header packet diagram
The 8-byte chunk header is too small for byte-level units (cells are
unreadably tiny on the 32-unit row). Bit-level gives 2 well-proportioned
rows of 32 bits each with readable labels.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
