Nx backend implementation that delegates tensor operations to Burn via NIF.

This module implements the Nx.Backend behaviour, translating Nx tensor operations into calls to the Rust NIF layer which executes them using Burn's CubeCL backend for GPU acceleration.

Architecture

Axon model
   ↓
Nx.Defn graph
   ↓
ExBurn.Backend (Nx.Backend behaviour)
   ↓
ExBurn.Nif (Rustler NIF) ←→ ExCubecl (GPU buffers, kernels, pipelines)
   ↓
Burn Autodiff<CubeCL> (Rust)
   ↓
CubeCL kernels
   ↓
Metal (iOS) / Vulkan (Android) / CUDA → GPU

Usage

Nx.default_backend(ExBurn.Backend)

Implementation Notes

• Tensors are stored as opaque NIF references on the Rust side
• Data is serialized as binary (f32 little-endian) for NIF calls
• The backend struct holds the NIF reference, shape, and type
• For performance-critical paths, use ExBurn.BurnBridge directly
• All public callbacks raise ExBurn.Error on failure