docs: DO NOT MERGE Mc/audit comments

[iAmMichaelConnor]

Just pushing my unfinished, WIP, disorganised review comments before Xmas.

Mainly for @LeilaWang to take a look at whenever you return to work :)

Noteworthy things:

• Lots of Q: , TODO: , AUDIT_COMMENT: comments littered through the code as I read.
• Some new comments.
  • Note: many of these are already staged into a separate PR: docs: misc extra protocol circuit comments #19174 (this branch builds on top of that branch, assuming the new comments aren't controversial).
• Some corrected comments.
• An ABOUT.md file, which summarises what all the rollup circuits do, and will hopefully be useful to external auditors (and will be useful to me whenever I return back to the rollup circuits).
• A simple draw.io diagram. Better diagrams are in the works, for my own personal tracking of the logic, but won't be ready until mid-January.
• A blobs hackmd (separate) which summarises the blob subprotocol, in case you want to give it to any external reviewers.
• Code changes
  • My intention is to cherry-pick each of these things into their own small PR:
    • Some extra field.nr and point.nr tests.
    • Removed some unused functions.
• Some reports from Claude:
  • Criticisms of arrays.nr (I imagine Claude will be able to rectify these)
  • Summaries of domain separators, including hashes which are missing domain separators.
    • A painful project for January.