Updates for v6

[jpmonette]

Modernized tooling, improved type safety, and cleaned up the codebase.

What Changed

• Jest → Vitest - faster tests, native TS/ESM
• ESLint + Prettier → Biome - one tool instead of two
• Removed 13 unused deps - eslint, prettier, jest, ts-jest, coveralls, etc.
• Replaced any types - proper types for XML and JSON structures
• Improved sanitization - sanitizeUrl() validates and normalizes URLs
• Modernized syntax - optional chaining, template literals, const, regular class methods
• Consolidated CI - 4 workflow files → 1