[Data] batch_ablation: create --out dir before writing ablation.json

A fresh --out path crashed the final write (night2 gate run) after all
cells had already printed; the tables survived only in the tee'd log.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Signed-off-by: Aarrya <aarrya.saraf@anyscale.com>

Author: AarryaSaraf

release/nightly_tests/dataset/arrow_rs_probe/batch_ablation.py

@@ -337,6 +337,7 @@ def orchestrate(a):
                     f"{r['rows']:>9}  {rr:>5} {rw:>6}  {gates}"
                 )
 
+    os.makedirs(os.path.dirname(os.path.abspath(out_path)), exist_ok=True)
     with open(out_path, "w") as fh:
         json.dump({"cells": results, "verdict": verdict}, fh, indent=2)
     fails = {k: v for k, v in verdict.items() if not v["passed"]}