Pure semantics of sequential GraphSpec chains

The interpreter splits the typed parameter pack at each sequential composition and applies the two subchains in order. It is intentionally direct, so proofs about chains need not pass through their SSA/DAG representation.

def NN.GraphSpec.Interp.spec {ps : List Spec.Shape} {σ τ : Spec.Shape} (g : Chain ps σ τ) {α : Type} [TorchLean.Storage α] [Context α] : TorchLean.TensorPack α ps → TorchLean.Tensor α σ → TorchLean.Tensor α τ

Pure tensor semantics of a sequential Chain.