llm improvements

- document the tokenizer used (https://github.com/huggingface/swift-transformers)
- provide a hook for tokenizer configuration, prompt augmentation
	- this isn't as rich as the python equivalents but it helps a little

Libraries/LLM/Models.swift

@@ -0,0 +1,107 @@
+// Copyright © 2024 Apple Inc.
+
+import Foundation
+
+/// Registry of models and and any overrides that go with them, e.g. prompt augmentation.
+/// If asked for an unknown configuration this will use the model/tokenizer as-is.
+///
+/// The python tokenizers have a very rich set of implementations and configuration.  The
+/// swift-tokenizers code handles a good chunk of that and this is a place to augment that
+/// implementation, if needed.
+public struct ModelConfiguration {
+    public let id: String
+    
+    /// overrides for TokenizerModel/knownTokenizers -- useful before swift-transformers is updated
+    public let overrideTokenizer: String?
+    
+    /// custom preparation logic for the prompt.  custom tokenizers provide more capability, but this
+    /// allows some minor formtting changes, e.g. wrapping the user input in the expected prompt
+    /// format
+    private let preparePrompt: ((String) -> String)?
+    
+    public init(id: String, overrideTokenizer: String? = nil, preparePrompt: ((String) -> String)? = nil) {
+        self.id = id
+        self.overrideTokenizer = overrideTokenizer
+        self.preparePrompt = preparePrompt
+    }
+    
+    public func prepare(prompt: String) -> String {
+        preparePrompt?(prompt) ?? prompt
+    }
+    
+    public static var registry = [String:ModelConfiguration]()
+    
+    public static func register(configurations: [ModelConfiguration]) {
+        bootstrap()
+        
+        for c in configurations {
+            registry[c.id] = c
+        }
+    }
+    
+    public static func configuration(id: String) -> ModelConfiguration {
+        bootstrap()
+
+        if let c = registry[id] {
+            return c
+        } else {
+            return ModelConfiguration(id: id)
+        }
+    }
+}
+
+extension ModelConfiguration {
+    
+    static let mistral7B4bit = ModelConfiguration(id: "mlx-community/Mistral-7B-v0.1-hf-4bit-mlx")
+
+    static let codeLlama13b4bit = ModelConfiguration(
+        id: "mlx-community/CodeLlama-13b-Instruct-hf-4bit-MLX",
+        overrideTokenizer: "PreTrainedTokenizer")
+    { prompt in
+        // given the prompt: func sortArray(_ array: [Int]) -> String { <FILL_ME> }
+        // the python code produces this (via its custom tokenizer):
+        // <PRE> func sortArray(_ array: [Int]) -> String {  <SUF> } <MID>
+        
+        "<PRE> " +
+        prompt.replacingOccurrences(of: "<FILL_ME>", with: "<SUF>") +
+        " <MID>"
+    }
+    
+    static let phi4bit = ModelConfiguration(id: "mlx-community/phi-2-hf-4bit-mlx") { prompt in
+        "Instruct: \(prompt). Output: "
+    }
+    
+    static let gemma2bQuantized = ModelConfiguration(
+        id: "mlx-community/quantized-gemma-2b-it",
+        overrideTokenizer: "PreTrainedTokenizer") { prompt in
+            "<start_of_turn>user \(prompt)<end_of_turn><start_of_turn>model"
+        }
+
+    private enum BootstrapState {
+        case idle
+        case bootstrapping
+        case bootstrapped
+    }
+    
+    static private var bootstrapState = BootstrapState.idle
+    
+    static func bootstrap() {
+        switch bootstrapState {
+        case .idle:
+            bootstrapState = .bootstrapping
+            register(configurations: [
+                mistral7B4bit,
+                codeLlama13b4bit,
+                phi4bit,
+                gemma2bQuantized,
+            ])
+            bootstrapState = .bootstrapped
+
+        case .bootstrapping:
+            break
+            
+        case .bootstrapped:
+            break
+        }
+    }
+}