fix(core) request_permissions tool flakey test

[dylan-hurd-oai]

Summary

Fixes a flaky macOS codex-core test:

approved_folder_write_request_permissions_unblocks_later_apply_patch

The test had two sources of nondeterminism:

1. It inherited the ambient approvals_reviewer config when the test did not explicitly pass one. On
   machines configured with auto_review, the request_permissions tool call could be routed through
   Guardian instead of emitting the RequestPermissions event the test expected.
2. expect_request_permissions_event treated any TurnComplete as a failure while waiting for the
   permissions request. In practice, unrelated completion events can be observed before the specific
   permissions event, causing the test to fail even though the expected request may still arrive.

This change makes the test deterministic by defaulting test turns to ApprovalsReviewer::User unless a
subcase explicitly overrides it, and by waiting for the specific RequestPermissions call id. The strict
auto-review subcase also now provides two mocked Guardian allow responses, matching the two review
requests made on that path.

Testing

Ran the test 5 times:
cargo test -p codex-core --test all approved_folder_write_request_permissions_unblocks_later_apply_patch -- --nocapture

[github-actions]

Closing this pull request because it has had no updates for more than 14 days. If you plan to continue working on it, feel free to reopen or open a new PR.