chore: add hash and encoding test vectors

[kudala-bharani]

What and why

Closes #98.

Adds the requested reference vectors for MD5 and the encoding helpers. This covers empty input, the 55/56/64-byte MD5 padding boundaries, all five hash keys and digests, partial Ascii85 groups, zero-byte abbreviation, hex formatting, line wrapping, byte sizes, and shell/SQL quoting.

The MD5 boundary values were generated once with Node's crypto.createHash and stored as constants. Ascii85 vectors were also checked against Python's standard-library encoder. No production code changes were needed.

Type of change

• Test coverage

Checklist

• npm run lint && npm run test && npm run build passes locally
• Tests live in lib/__tests__/; no production logic changes
• No analytics, trackers, or calls that send user data off-device
• Works in both light and dark themes (not applicable; no UI changes)

Notes for reviewers

One test file changed, with 29 new test cases. On Node 22.23.3, all 56 tests pass and the production build succeeds. Lint exits successfully with 13 existing warnings in unchanged files; the modified test file has no warnings.

[anurag629]

Hey @kudala-bharani, really nice work! I checked the MD5 padding values with Node's crypto and the Ascii85 ones with Python, all of them match. This covers everything in #98.

Small thing for next time, drop a comment on the issue first so I can assign it to you. Saves two people from doing the same work.

If you want to pick up another one, just comment on any open hacktoberfest issue and I'll assign it to you.