fix: resolve all 16 failing tests in utility library

[stooit]

Summary

• Fixed 16 failing tests across 5 source files without modifying any test files
• All 60 tests now pass (previously 44 pass / 16 fail)

Changes

File	Fix
src/calculator.ts	Throw error on division by zero instead of returning Infinity
src/string-utils.ts	Fix wordCount to handle multiple consecutive spaces; implement truncate with word-boundary support
src/task-manager.ts	Implement remove, update, and sortBy methods
src/date-utils.ts	Use Math.round for day calculation in formatRelative (fixes 36h to 2 days ago)
src/validator.ts	Allow TLDs up to 63 chars in email validation; support port numbers in URL validation

Assumptions

• sortBy priority uses high > medium > low ordering
• sortBy createdAt sorts oldest first
• truncate prefers word boundaries but falls back to hard truncation at maxLength-3
• Division by zero throws a generic Error with message Division by zero