fix: pass all failing tests in utility library

[stooit]

Summary

Fixes all 16 previously-failing tests across 5 source files. The full suite now passes: 60 pass / 0 fail. No test files were modified and no dependencies were added.

Changes

• src/calculator.ts — divide now throws Error("Division by zero") instead of returning Infinity.
• src/string-utils.ts — wordCount splits on /\s+/ to handle consecutive spaces; truncate implemented (returns input when within limit, otherwise cuts at the last word boundary with the ellipsis counted toward maxLength, and handles strings shorter than the ellipsis).
• src/task-manager.ts — implemented the missing remove, update, and sortBy methods (sortBy orders priority high→medium→low and createdAt oldest-first; remove/update return false for unknown ids).
• src/validator.ts — isEmail now accepts long TLDs (e.g. user@example.museum); isUrl accepts URLs with ports (e.g. http://localhost:3000).
• src/date-utils.ts — fixed formatRelative rounding so 36h reads "2 days ago" and the hours branch uses Math.floor, so it can never emit "24 hours ago".

Testing

bun test → 60 pass, 0 fail, 70 expect() calls.

Assumptions

• Treated the test files as the authoritative spec for each function's contract.
• Applied one out-of-strict-scope but trivial correctness fix (the Math.floor 24h-boundary guard in formatRelative) surfaced during review; it changes no tested behaviour.

🤖 Generated autonomously.