Explore build-phase support in .rezn files

[andreamancuso]

It might be worth exploring support for a build block inside .rezn files that can:

Clone a repo (git)

Run arbitrary build commands (e.g., make, cargo build)

Extract artifacts (e.g., binary paths)

Package the result into a minimal runtime container

This would let .rezn files act as self-contained deployment units — handling both build and runtime config — similar to multi-stage Docker builds, but fully controlled via the DSL.

We’d need to think through:

Sandbox/container for the build phase

Output path handling

Optional caching

Security implications

How/where the final image is stored or tagged