Promote --moe-backend=flashinfer_cutedsl to the batched NVFP4 backend when the selected all2all path requires batched expert activations, and make flashinfer_nvlink_one_sided prepare/finalize speak the batched expert contract.
Also add regression coverage for the backend selection and one-sided regroup/reduce helpers.
Co-authored-by: OpenAI Codex <codex@openai.com>
Signed-off-by: Roger Wang <hey@rogerw.io>