handle partially quantized models (#76)

* handle partially quantized models

- fix for #53 #71 #69 #74
- in order to test the models
	- I added a default prompt of an appropriate form
	- while working on the model configuration also added additional stop tokens (#74)
- fixed the repetitionPenalty code (#71)

Libraries/LLM/Models.swift

@@ -33,6 +33,12 @@ public struct ModelConfiguration {
     /// overrides for TokenizerModel/knownTokenizers -- useful before swift-transformers is updated
     public let overrideTokenizer: String?
 
+    /// A reasonable default prompt for the model
+    public let defaultPrompt: String
+
+    /// Additional tokens to use for end of string
+    public let extraEOSTokens: Set<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
@@ -40,21 +46,29 @@ public struct ModelConfiguration {
 
     public init(
         id: String, tokenizerId: String? = nil, overrideTokenizer: String? = nil,
+        defaultPrompt: String = "hello",
+        extraEOSTokens: Set<String> = [],
         preparePrompt: ((String) -> String)? = nil
     ) {
         self.id = .id(id)
         self.tokenizerId = tokenizerId
         self.overrideTokenizer = overrideTokenizer
+        self.defaultPrompt = defaultPrompt
+        self.extraEOSTokens = extraEOSTokens
         self.preparePrompt = preparePrompt
     }
 
     public init(
         directory: URL, tokenizerId: String? = nil, overrideTokenizer: String? = nil,
+        defaultPrompt: String = "hello",
+        extraEOSTokens: Set<String> = [],
         preparePrompt: ((String) -> String)? = nil
     ) {
         self.id = .directory(directory)
         self.tokenizerId = tokenizerId
         self.overrideTokenizer = overrideTokenizer
+        self.defaultPrompt = defaultPrompt
+        self.extraEOSTokens = extraEOSTokens
         self.preparePrompt = preparePrompt
     }
 
@@ -98,11 +112,16 @@ public struct ModelConfiguration {
 extension ModelConfiguration {
 
     public static let mistral7B4bit = ModelConfiguration(
-        id: "mlx-community/Mistral-7B-v0.1-hf-4bit-mlx")
+        id: "mlx-community/Mistral-7B-v0.1-hf-4bit-mlx",
+
+        // https://www.promptingguide.ai/models/mistral-7b
+        defaultPrompt: "describe the swift language"
+    )
 
     public static let codeLlama13b4bit = ModelConfiguration(
         id: "mlx-community/CodeLlama-13b-Instruct-hf-4bit-MLX",
-        overrideTokenizer: "PreTrainedTokenizer"
+        overrideTokenizer: "PreTrainedTokenizer",
+        defaultPrompt: "func sortArray(_ array: [Int]) -> String { <FILL_ME> }"
     ) { prompt in
         // given the prompt: func sortArray(_ array: [Int]) -> String { <FILL_ME> }
         // the python code produces this (via its custom tokenizer):
@@ -111,13 +130,17 @@ extension ModelConfiguration {
         "<PRE> " + prompt.replacingOccurrences(of: "<FILL_ME>", with: "<SUF>") + " <MID>"
     }
 
-    public static let phi4bit = ModelConfiguration(id: "mlx-community/phi-2-hf-4bit-mlx") {
-        prompt in
-        "Instruct: \(prompt)\nOutput: "
-    }
+    public static let phi4bit = ModelConfiguration(
+        id: "mlx-community/phi-2-hf-4bit-mlx",
+
+        // https://www.promptingguide.ai/models/phi-2
+        defaultPrompt: "Why is the sky blue?"
+    )
 
     public static let phi34bit = ModelConfiguration(
-        id: "mlx-community/Phi-3-mini-4k-instruct-4bit-no-q-embed"
+        id: "mlx-community/Phi-3-mini-4k-instruct-4bit-no-q-embed",
+        defaultPrompt: "what is the gravity on mars and the moon?",
+        extraEOSTokens: ["<|end|>"]
     ) {
         prompt in
         "<s><|user|>\n\(prompt)<|end|>\n<|assistant|>\n"
@@ -125,26 +148,35 @@ extension ModelConfiguration {
 
     public static let gemma2bQuantized = ModelConfiguration(
         id: "mlx-community/quantized-gemma-2b-it",
-        overrideTokenizer: "PreTrainedTokenizer"
+        overrideTokenizer: "PreTrainedTokenizer",
+
+        // https://www.promptingguide.ai/models/gemma
+        defaultPrompt: "what is the difference between lettuce and cabbage?"
+
     ) { prompt in
         "<start_of_turn>user \(prompt)<end_of_turn><start_of_turn>model"
     }
 
     public static let qwen205b4bit = ModelConfiguration(
         id: "mlx-community/Qwen1.5-0.5B-Chat-4bit",
-        overrideTokenizer: "PreTrainedTokenizer"
+        overrideTokenizer: "PreTrainedTokenizer",
+        defaultPrompt: "why is the sky blue?"
     ) { prompt in
         "<|im_start|>system\nYou are a helpful assistant<|im_end|>\n<|im_start|>user\n\(prompt)<|im_end|>\n<|im_start|>assistant"
     }
 
     public static let openelm270m4bit = ModelConfiguration(
-        id: "mlx-community/OpenELM-270M-Instruct"
+        id: "mlx-community/OpenELM-270M-Instruct",
+
+        // https://huggingface.co/apple/OpenELM
+        defaultPrompt: "Once upon a time there was"
     ) { prompt in
         "\(prompt)"
     }
 
     public static let llama38B4bit = ModelConfiguration(
-        id: "mlx-community/Meta-Llama-3-8B-Instruct-4bit"
+        id: "mlx-community/Meta-Llama-3-8B-Instruct-4bit",
+        defaultPrompt: "what is the difference between a fruit and a vegetable?"
     ) {
         prompt in
         "<|begin_of_text|><|start_header_id|>system<|end_header_id|>\nYou are a helpful assistant<|eot_id|>\n<|start_header_id|>user<|end_header_id|>\n\(prompt)<|eot_id|>\n<|start_header_id|>assistant<|end_header_id|>"