deps: Replace vergen with a new support crate

[smalis-msft]

The vergen crate, and especially its new version 9, pulls in a lot of dependencies for the relatively small pieces of it we use. Replace it with a new home-grown crate that has no dependencies beyond anyhow and just does what we need.

[github-actions]

⚠️ Unsafe Code Detected

This PR modifies files containing unsafe Rust code. Extra scrutiny is required during review.

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[Copilot]

Pull request overview

This PR removes the vergen dependency and replaces it with a small in-repo build-script helper crate that emits git SHA/branch information via cargo:rustc-env, reducing transitive dependency footprint while preserving build metadata.

Changes:

• Add new support/build_rs_git_info crate to emit BUILD_GIT_SHA / BUILD_GIT_BRANCH using the git CLI.
• Update OpenHCL crates’ build.rs and runtime code to use the new env var names instead of VERGEN_*.
• Remove vergen from workspace dependencies and lockfile.

Reviewed changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
support/build_rs_git_info/src/lib.rs	New helper implementation for invoking git and emitting build env vars.
support/build_rs_git_info/Cargo.toml	Defines the new support crate and its minimal dependencies.
openhcl/underhill_init/src/lib.rs	Switch runtime logging to BUILD_GIT_SHA / BUILD_GIT_BRANCH.
openhcl/underhill_init/build.rs	Use build_rs_git_info instead of vergen.
openhcl/underhill_init/Cargo.toml	Replace vergen build-dependency with build_rs_git_info.
openhcl/underhill_crash/src/lib.rs	Switch crash metadata to BUILD_GIT_SHA.
openhcl/underhill_crash/build.rs	Use build_rs_git_info instead of vergen.
openhcl/underhill_crash/Cargo.toml	Replace vergen build-dependency with build_rs_git_info.
openhcl/build_info/src/lib.rs	Switch BuildInfo fields to read BUILD_GIT_SHA / BUILD_GIT_BRANCH.
openhcl/build_info/build.rs	Use build_rs_git_info instead of vergen.
openhcl/build_info/Cargo.toml	Replace vergen build-dependency with build_rs_git_info.
Cargo.toml	Add build_rs_git_info workspace dep; remove vergen version.
Cargo.lock	Lockfile updates reflecting dependency removal/addition.

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[github-actions]

At least one Petri test failed.

[Copilot]

Pull request overview

Copilot reviewed 12 out of 13 changed files in this pull request and generated 1 comment.

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