Bun 1.4 rewrites from Zig to Rust, cuts memory by up to 48%

Bun 1.4 rewrites the runtime from Zig to Rust, adds 1,517 Node.js test suite passes, and cuts memory usage by up to 48% for HTTP servers. It also reduces idle CPU usage by 5x and starts 50% faster on Linux. New APIs include Bun.Image, Bun.WebView, Bun.cron(), and Bun.Terminal.