Modernizing the toolbox for Cloudflare Pages builds

What this post added

Introduced a new beta build system for Cloudflare Pages with updated default versions of Node.js, Python, and Ruby, and added support for pnpm. Re-architected the build system from a monolithic Kubernetes container to a modular approach using sequential init containers, improving isolation between system and user stages. This modularity enables future features like build caching. Rearchitected build log streaming to use a global log collector container.