Make-so the js bundles are faster to build, by switching from webpack+babel to rspack (or other fast alternative)

[Venryx]

Some possible bundlers:

• rspack + swc
• swc (ie. its own bundler)
• esbuild

The current plan is to try to use RSPack, since it seems to be the most mature of the solutions that are in the new-generation "fast group". (turbopack looks great, but they still have not added good support for non-nextjs webpack users to migrate over)