fix: box apply_patch test harness futures (#15835)

## 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

- #12768
- #13429

codex-rs/core/tests/common/test_codex.rs

@@ -792,7 +792,9 @@ impl TestCodexHarness {
     }
 
     pub async fn submit(&self, prompt: &str) -> Result<()> {
-        self.test.submit_turn(prompt).await
+        // Box the submit-and-wait path so callers do not inline the full turn
+        // future into their own async state.
+        Box::pin(self.test.submit_turn(prompt)).await
     }
 
     pub async fn submit_with_policy(
@@ -844,13 +846,17 @@ impl TestCodexHarness {
         call_id: &str,
         output_type: ApplyPatchModelOutput,
     ) -> String {
+        // Box the awaited output helpers so callers do not inline request
+        // capture and response parsing into their own async state.
         match output_type {
-            ApplyPatchModelOutput::Freeform => self.custom_tool_call_output(call_id).await,
+            ApplyPatchModelOutput::Freeform => {
+                Box::pin(self.custom_tool_call_output(call_id)).await
+            }
             ApplyPatchModelOutput::Function
             | ApplyPatchModelOutput::Shell
             | ApplyPatchModelOutput::ShellViaHeredoc
             | ApplyPatchModelOutput::ShellCommandViaHeredoc => {
-                self.function_call_stdout(call_id).await
+                Box::pin(self.function_call_stdout(call_id)).await
             }
         }
     }