--frozen builds?

In CI you should be building off your lockfile and not bothering to fetch the registry (which takes forever these days...). We should probably add support for --locked and/or --frozen to cargo-dist and have CI use it to make builds faster and more reliable. Not sure how that might impact cargo-metadata if at all.

Probably we shouldn't default to using these flags, since when running locally we want things to Just Work (although we *should* try to properly forward the "updating registry" printout from Cargo because it looks like we're just hanging otherwise...)

Start by tracing how cargo-dist invokes Cargo in CI and how cargo-metadata is affected. Compare the behavior of Cargo's --locked and --frozen flags, then verify that CI avoids unnecessary registry fetches while local builds keep their current defaults and registry-update output remains visible.

Written by the indexing model from the issue text.