elementwise.rs: added broadcast_col_binary CUDA kernel for [N,M]*[N,1]
gpu_tensor.rs: broadcast_mul/broadcast_div now handle column broadcast
stream_ops.rs: gpu_cat_dim1 extended for 3D tensors
branching.rs: NoisyLinear weights registered in GpuVarStore
noisy_layers.rs: register_in_store() method for weight registration
distributional_dueling.rs: NoisyLinear weight registration
dqn.rs: checkpoint load wires weights into VarStore
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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