Add Apple Silicon (MPS) support to inference scripts

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Summary

• Make the ReCo inference entry points (inference_reco_single.py, inference_reco_single_ref.py, tools/step_1_inference_vace_diffusers_unip.py) runnable on Apple Silicon by targeting PyTorch's mps backend instead of cuda.
• Switch the default dtype on the MPS path from bfloat16 to float16 (bfloat16 still has incomplete coverage on MPS) and replace the CUDA-only seeding (torch.cuda.manual_seed, torch.backends.cudnn.*) with torch.mps.manual_seed.
• Set PYTORCH_ENABLE_MPS_FALLBACK=1 so any operator that isn't yet MPS-native transparently falls back to CPU instead of erroring out.
• Add a tiny smoke-test config assets/replace_test_mps.txt containing a single short-video prompt to make it easy to verify the replace task end-to-end on a Mac.

Why

The current entry points hard-code device=\"cuda\" and torch_dtype=torch.bfloat16, which prevents any inference on M-series Macs. None of the changes alter the CUDA code path semantically aside from the dtype default, and device is still passed through args, so CUDA users can keep using device=\"cuda\"/bfloat16 unchanged.

Test plan

• python inference_reco_single.py --task_name replace --test_txt_file_name assets/replace_test_mps.txt --lora_ckpt all_ckpts/ReCo_ori_rank128-2025_m12_version.ckpt on an M-series Mac with PyTorch >= 2.5 produces an output video without throwing a device/dtype error.
• Existing CUDA runs are unaffected when the user passes device=\"cuda\" (no changes to that branch).

Notes for reviewers

• This is the entry-point half of the MPS port. Functional execution also requires complementary patches inside the vendored DiffSynth-Studio/ submodule (forcing PyTorch SDPA over flash-attn, etc.). Those live in a separate change because DiffSynth-Studio is a vendored upstream project.
• This PR has not yet been verified end-to-end against a finished inference run; the Wan2.1-VACE-1.3B weight download was still in progress when the PR was opened. Marking as draft-ready for early review of the entry-point delta.

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