bazel: more hygenic build deps

[ParkMyCar]

This PR changes our Bazel build so the dependencies we use in build scripts are more hygenic. Specifically, it moves the codegen module from the ore crate into a new ore-build crate, and tweaks our generated BUILD.bazel files.

Bazel builds a Cargo Build Script, and it's dependencies, in the exec configuration which is the config for the host currently running the build. So when a crate is used in a build script it generally gets built twice, once for the platform the build is targeting, and once for the host running the build. Previously we were using the ore crate in a few build scripts, which results in ore and all of it's dependencies being build twice. With remote caching this isn't too bad, but it resulted in unnecessary fetching from S3, and when ore is changed, unnecessary re-building.

When building environmentd, clusterd, and balancerd at the same time, the number of Bazel actions is reduced from 4,692 to 3,947.

Motivation

Faster builds

Tips for reviewers

Just review the first commit, the second is just the changes from running bin/bazel gen

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.

[def-]

No complaints from QA side, but I don't know enough about Rust building to fully approve,

[aljoscha]

🙌