docs: ctpop NatSpec, accurate H01 comment, correct README publish section

[thedavidmeister]

Closes #22
Closes #23
Closes #27
Closes #28

Documentation-only batch over src/lib/LibCtPop.sol and the README:

• [ctpop-missing-natspec] [LOW] ctpop() has no @param/@return NatSpec #22 / [ctpopslow-missing-natspec] [INFO] ctpopSlow() has no @param/@return NatSpec #27: ctpop() and ctpopSlow() gain @param/@return NatSpec.
• [h01-comment-imprecise] [INFO] CTPOP_H01 comment '1 bytes for ctpop' is broken/uninformative #28: the CTPOP_H01 comment (1 bytes for ctpop) now states what the constant actually does: every byte set to 0x01 so the SWAR multiply sums the per-byte bit counts into the top byte, which the final >> 248 extracts.
• [readme-publish-section-stale] [LOW] README Publish section: dead workflow link + wrong trigger #23: the README Publish section linked a nonexistent publish-soldeer.yaml and told contributors to tag v<x.y.z>; the actual workflow is Package Release, triggered on push to main, delegating to rainix's reusable autopublish with soldeer-package: rain-math-binary.

QA

• No executable behavior changes — comments and README only; forge fmt --check clean and the full suite is 6/6 green at this head (nix develop github:rainlanguage/rainix#sol-shell -c forge test), identical to base.
• Oracle for each new doc claim, verified against the code rather than copied from it:
  • The H01 comment's SWAR claim matches x = (x * CTPOP_H01) >> 248 and explains why the type(uint256).max case is special-cased (a count of 256 overflows the top byte).
  • The @return wording ("number of bits set") is the Hamming-weight definition the file already cites.
  • The README claims are read directly from .github/workflows/package-release.yaml: on: push: branches: [main], workflow name Package Release, explicit soldeer-package: rain-math-binary input.
• Category check: [ctpop-missing-natspec] [LOW] ctpop() has no @param/@return NatSpec #22/[ctpopslow-missing-natspec] [INFO] ctpopSlow() has no @param/@return NatSpec #27 name the two undocumented functions (both documented); [h01-comment-imprecise] [INFO] CTPOP_H01 comment '1 bytes for ctpop' is broken/uninformative #28 names the one broken constant comment (rewritten); [readme-publish-section-stale] [LOW] README Publish section: dead workflow link + wrong trigger #23 names the two README errors — dead link and wrong trigger (both corrected). Nothing else in the section drifted.

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📥 Commits

Reviewing files that changed from the base of the PR and between 208336a and 90244af.

📒 Files selected for processing (2)

• README.md
• src/lib/LibCtPop.sol

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 2026-07-18-docs-natspec-readme

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[thedavidmeister]

🤖 ai:vetter
Reviewed 90244af: ready — closes #22 #23 #27 #28 — NatSpec for both ctpop fns, accurate H01 SWAR comment, README publish section verified against package-release.yaml (push-to-main, rain-math-binary)
cost 68 — docs-only, claims checked vs workflow