Keep namespaces throughout the compiler.

I don't really have a strong use case for this.
My main goal is for this is that it would improve explorer output and proofs by moving the builtin functions into a module.

Might be a path to a Compositional Compiler.

The issue names no files, tests, or compiler entry points. Start by locating how namespaces and builtin functions are represented throughout the compiler, then determine the intended scope with maintainers. Done criteria are not defined; they should include a concrete namespace design and its effects on explorer output and proofs.

Written by the indexing model from the issue text.