Performance Improvements

• about ~15-20% faster build (can go up for 30-50% as noted in CI) 🔥
• functional programming to ensure no side-effects ⚙️
• splits & organises files for easier development in future 📦
• provides hook for each loaded config 👁️
• drops requireModule for await import() (also parallelised) 🚢

Amazing work done by @ineshbose in #690