fix: implement missing utilities and fix edge-case bugs

[stooit]

Summary

Fixes all 16 previously failing tests across the utility library — implementing missing functionality and correcting edge-case bugs. All 60 tests now pass (0 fail); no test files were modified and no dependencies were added.

Changes by file

• src/calculator.ts — divide now throws on division by zero instead of returning Infinity.
• src/date-utils.ts — formatRelative uses round semantics so 36h → "2 days ago"; hour value capped at 23 to avoid emitting "24 hours ago".
• src/string-utils.ts — wordCount collapses consecutive whitespace ("hello world" → 2); truncate implemented (word-boundary truncation, "..." counts toward maxLength, leading-space handling).
• src/validator.ts — isEmail accepts long TLDs (.museum); isUrl accepts URLs with ports (http://localhost:3000).
• src/task-manager.ts — implemented remove, update, and sortBy (priority high>medium>low, createdAt oldest-first, status).

Testing

bun test → 60 pass, 0 fail.

Notes / assumptions

• Fixed only what the tests require, plus two low-risk hardening tweaks flagged in review (truncate leading-space trim, hour cap) — both verified against the full suite.
• Changes were reviewed by a code-review pass and confirmed sound.

🤖 Generated autonomously.