fix: box apply_patch test harness futures

[bolinfest]

Why

#[large_stack_test] made the apply_patch_cli tests pass by giving them more stack, but it did not address why those tests needed the extra stack in the first place.

The real problem is the async state built by the apply_patch_cli harness path. Those tests await three helper boundaries directly: harness construction, turn submission, and apply-patch output collection. If those helpers inline their full child futures, the test future grows to include the whole harness startup and request/response path.

This change replaces the workaround from #12768 with the same basic approach used in #13429, but keeps the fix narrower: only the helper boundaries awaited directly by apply_patch_cli stay boxed.

What Changed

• removed #[large_stack_test] from core/tests/suite/apply_patch_cli.rs
• restored ordinary #[tokio::test(flavor = "multi_thread", worker_threads = 2)] annotations in that suite
• deleted the now-unused codex-test-macros crate and removed its workspace wiring
• boxed only the three helper boundaries that the suite awaits directly:
  • apply_patch_harness_with(...)
  • TestCodexHarness::submit(...)
  • TestCodexHarness::apply_patch_output(...)
• added comments at those boxed boundaries explaining why they remain boxed

Testing

• cargo test -p codex-core --test all suite::apply_patch_cli -- --nocapture

References

• feat: add large stack test macro #12768
• core: box wrapper futures to reduce stack pressure #13429