Record Git metadata to rollout (#1598)

# Summary

- Writing effective evals for codex sessions requires context of the
overall repository state at the moment the session began
- This change adds this metadata (git repository, branch, commit hash)
to the top of the rollout of the session (if available - if not it
doesn't add anything)
- Currently, this is only effective on a clean working tree, as we can't
track uncommitted/untracked changes with the current metadata set.
Ideally in the future we may want to track unclean changes somehow, or
perhaps prompt the user to stash or commit them.

# Testing
- Added unit tests
- `cargo test && cargo clippy --tests && cargo fmt -- --config
imports_granularity=Item`

### Resulting Rollout
<img width="1243" height="127" alt="Screenshot 2025-07-17 at 1 50 00 PM"
src="https://github.com/user-attachments/assets/68108941-f015-45b2-985c-ea315ce05415"
/>

codex-rs/core/src/codex.rs

@@ -594,7 +594,7 @@ async fn submission_loop(
                 let mut restored_items: Option<Vec<ResponseItem>> = None;
                 let rollout_recorder: Option<RolloutRecorder> =
                     if let Some(path) = resume_path.as_ref() {
-                        match RolloutRecorder::resume(path).await {
+                        match RolloutRecorder::resume(path, cwd.clone()).await {
                             Ok((rec, saved)) => {
                                 session_id = saved.session_id;
                                 if !saved.items.is_empty() {