Reduce sub-sub-sub dependencies

[pi0]

Context: from es-tooling/module-replacements#60 (comment) by @AbhiPrasad

Currently unbuilds install lots of sub-dependencies some are not required for basic builds. (graph)

From CSS stuff, I assume they are related to mkdist optional loaders and I think we can replace them with optional peer dependencies (as part of #381 migration) and even a simple smart prompt to install if needed.

Rollup and its plugins are also a pain point. While inlining them all is one option, perhaps we can wait for rolldown to be mature and swap to it in v4.