[codex] fix compressed rollout fixture SessionMeta initialization (#25628)

## Summary
- initialize `parent_thread_id` in the compressed rollout test fixture's
`SessionMeta`
- restore rollout test compilation across Bazel test, clippy,
release-build, and argument-comment-lint jobs

## Root cause
PR #25087 (`Read compressed rollouts and materialize before append`)
added `codex-rs/rollout/src/compression_tests.rs` in merge commit
`a8a6071279b6f3112fcc5fc3fee69c48473d7149`. Its `write_rollout` fixture
constructs `SessionMeta` without the required `parent_thread_id` field,
causing `error[E0063]` when Bazel compiles `rollout-unit-tests-bin` on
`main` and downstream PRs.

## Validation
- `UV_CACHE_DIR=/private/tmp/codex-uv-cache just fmt`
- `just test -p codex-rollout` (`59` tests passed; bench smoke passed)
- `git diff --check`
- manually audited the touched Rust diff for positional literal argument
comments; the change adds no positional callsite

## Local lint blocker
- `just argument-comment-lint` could not reach source inspection locally
because Bazel's LLVM dependency fails analysis:
`compiler-rt/BUILD.bazel` glob `include/sanitizer/*.h` matched no files.

codex-rs/rollout/src/compression_tests.rs

@@ -243,6 +243,7 @@ fn write_rollout(path: &std::path::Path, thread_id: ThreadId, message: &str) ->
         meta: SessionMeta {
             id: thread_id,
             forked_from_id: None,
+            parent_thread_id: None,
             timestamp: "2025-01-03T12:00:00Z".to_string(),
             cwd: parent.to_path_buf(),
             originator: "test".to_string(),