TorchLean-Executable GraphSpec Models

This module is the architecture-facing home for reusable model constructors that still execute via the TorchLean autograd runtime.

The split is intentional:

• NN.GraphSpec.Models.* contains graph-authored architectures and architecture-facing wrappers.
• NN.GraphSpec.Models.TorchLean.* contains executable TorchLean.NN.Seq / TorchLean.Program constructors for common models.
• NN.Runtime.Autograd.TorchLean.* contains runtime machinery: tensors, ops, backends, sessions, losses, optimizers, and training loops.

So users looking for models start from GraphSpec, while runtime internals stay focused on execution.