Port Orion to HEIR

The [Orion paper](https://arxiv.org/abs/2311.03470) has a PyTorch -> Lattigo lowering with some ML-specific CKKS packing strategies. We should port their work to HEIR. It would be a good start to arithmetic-FHE for ML in HEIR, and give us another front-end (via [torch-mlir](https://github.com/llvm/torch-mlir)), and a starting point for lowering meaningful programs to a CKKS dialect.

This would require at least:

- Having a recipe to go from PyTorch to TOSA (probably we don't need to integrate torch-mlir proper into this project)
- A Lattigo exit dialect with the relevant ops
- A lowering TOSA -> lattigo
- Somewhere to put the optimizations from the paper