chore: script to create a Rust release (#759)

For now, keep things simple such that we never update the `version` in
the `Cargo.toml` for the workspace root on the `main` branch. Instead,
create a new branch for a release, push one commit that updates the
`version`, and then tag that branch to kick off a release.

To test, I ran this script and created this release job:

https://github.com/openai/codex/actions/runs/14762580641

codex-rs/Cargo.lock

@@ -469,7 +469,7 @@ dependencies = [
 
 [[package]]
 name = "codex-cli"
-version = "0.0.2504301132"
+version = "0.0.0"
 dependencies = [
  "anyhow",
  "clap",
@@ -523,7 +523,7 @@ dependencies = [
 
 [[package]]
 name = "codex-exec"
-version = "0.0.2504301132"
+version = "0.0.0"
 dependencies = [
  "anyhow",
  "chrono",