Add Apple Silicon (MPS) support

[rbourgeat]

Issue: #5

This MR enables the TripoSG project to run on Apple Silicon (macOS) using PyTorch's MPS backend.

How to Run on macOS (Apple Silicon):

1. Enable MPS Fallback (Important):
   Before running any inference script, execute the following in your terminal:

export PYTORCH_ENABLE_MPS_FALLBACK=1

This is required because some 3D operations used during mesh extraction (e.g., max_pool3d_with_indices) are not yet natively supported on MPS and need to fall back to the CPU.

2. Example: Image-to-3D Inference:

python3 -m scripts.inference_triposg \
    --image-input assets/example_data/jkghed.png \ 
    --output-path ./output_macos_hierarchical.glb \
    --faces 5000 \
    --no-use-flash-decoder

(Note: --no-use-flash-decoder is recommended for MPS due to potential diso library compatibility and to ensure the CPU fallback path for hierarchical_extract_geometry (which now produces correct results with float32) is used.)

3. Example: Scribble-to-3D Inference:

python3 -m scripts.inference_triposg_scribble \
    --image-input assets/example_scribble_data/cat_with_wings.png \
    --prompt "a cat with wings" \
    --output-path ./output_macos_scribble.glb