implement LoRA / QLoRA (#46)

* implement LoRA / QLoRA

- example of using MLX to fine-tune an LLM with low rank adaptation (LoRA) for a target task
- see also https://arxiv.org/abs/2106.09685
- based on https://github.com/ml-explore/mlx-examples/tree/main/lora

* add some command line flags I found useful during use
- --quiet -- don't print decorator text, just the generated text
- --prompt @/tmp/file.txt -- load prompt from file

* user can specify path to model OR model identifier in huggingface

* update mlx-swift reference

Co-authored-by: Ashraful Islam <ashraful.meche@gmail.com>
Co-authored-by: JustinMeans <46542161+JustinMeans@users.noreply.github.com>

Package.swift

@@ -27,6 +27,7 @@ let package = Package(
                 .product(name: "MLX", package: "mlx-swift"),
                 .product(name: "MLXFast", package: "mlx-swift"),
                 .product(name: "MLXNN", package: "mlx-swift"),
+                .product(name: "MLXOptimizers", package: "mlx-swift"),
                 .product(name: "MLXRandom", package: "mlx-swift"),
                 .product(name: "Transformers", package: "swift-transformers"),
                 .product(name: "AsyncAlgorithms", package: "swift-async-algorithms"),
@@ -43,6 +44,7 @@ let package = Package(
                 .product(name: "MLX", package: "mlx-swift"),
                 .product(name: "MLXFast", package: "mlx-swift"),
                 .product(name: "MLXNN", package: "mlx-swift"),
+                .product(name: "MLXOptimizers", package: "mlx-swift"),
                 .product(name: "MLXRandom", package: "mlx-swift"),
                 .product(name: "Transformers", package: "swift-transformers"),
                 .product(name: "AsyncAlgorithms", package: "swift-async-algorithms"),