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>

Libraries/LLM/Lora+Data.swift

@@ -0,0 +1,61 @@
+// Copyright © 2024 Apple Inc.
+
+import Foundation
+
+enum LoRADataError: Error {
+    case fileNotFound(URL, String)
+}
+
+/// Load a LoRA data file.
+///
+/// Given a directory and a base name, e.g. `train`, this will load a `.jsonl` or `.txt` file
+/// if possible.
+public func loadLoRAData(directory: URL, name: String) throws -> [String] {
+    let extensions = ["jsonl", "txt"]
+
+    for ext in extensions {
+        let url = directory.appending(component: "\(name).\(ext)")
+        if FileManager.default.fileExists(atPath: url.path()) {
+            return try loadLoRAData(url: url)
+        }
+    }
+
+    throw LoRADataError.fileNotFound(directory, name)
+}
+
+/// Load a .txt or .jsonl file and return the contents
+public func loadLoRAData(url: URL) throws -> [String] {
+    switch url.pathExtension {
+    case "jsonl":
+        return try loadJSONL(url: url)
+
+    case "txt":
+        return try loadLines(url: url)
+
+    default:
+        fatalError("Unable to load data file, unknown type: \(url)")
+
+    }
+}
+
+func loadJSONL(url: URL) throws -> [String] {
+
+    struct Line: Codable {
+        let text: String?
+    }
+
+    return try String(contentsOf: url)
+        .components(separatedBy: .newlines)
+        .filter {
+            $0.first == "{"
+        }
+        .compactMap {
+            try JSONDecoder().decode(Line.self, from: $0.data(using: .utf8)!).text
+        }
+}
+
+func loadLines(url: URL) throws -> [String] {
+    try String(contentsOf: url)
+        .components(separatedBy: .newlines)
+        .filter { !$0.isEmpty }
+}