Tweaks to run dspy-produced calls to the server, with gemma template. (#810)

* Tweaks to run dspy-produced calls to the server, with gemma template.

following comment https://github.com/stanfordnlp/dspy/issues/385#issuecomment-1998939936

can try it out with:
```sh
python -m server --model mlx-community/gemma-1.1-7b-it-4bit --port 1143
```
modulo patching the relative imports in server.py
```
-from .tokenizer_utils import TokenizerWrapper
-from .utils import generate_step, load
+from mlx_lm.tokenizer_utils import TokenizerWrapper
+from mlx_lm.utils import generate_step, load
```

and then, ont the dspy side:
```python
import dspy
lm = dspy.OpenAI(model_type="chat", api_base="http://localhost:11434/v1/", api_key="not_needed", max_tokens=250)
lm("hello")
```

* simpler way to validate float or int

* remove logic that works around incompatible templates, too gemma specific

* tweak messages for common denominator

* use generate.py workaround for DBXR

* put behind flag

* oops

* Solution to chat template issue: pass in a custom template!

The template should likely adhere to the OpenAI chat model.
Here is such a template for Gemma.

--chat-template "{{ bos_token }}{% set extra_system = '' %}{% for message in messages %}{% if (message['role'] == 'assistant') %}{% set role = 'model' %}{% else %}{% set role = message['role'] %}{% endif %}{% if role == 'system' %}{% set extra_system = extra_system + message['content'] %}{% else %}{% if role == 'user' and extra_system %}{% set message_system = 'System: ' + extra_system %}{% else %}{% set message_system = '' %}{% endif %}{{ '<start_of_turn>' + role + '\n' + message_system + message['content'] | trim + '<end_of_turn>\n' }}{% endif %}{% endfor %}{% if add_generation_prompt %}{{'<start_of_turn>model\n'}}{% endif %}"

* remove convoluted solution

* Tweak for when None is provided explicitly, and must be set to [] too.

For example, the outlines library provides None explicitly.

* style

---------

Co-authored-by: Awni Hannun <awni@apple.com>

llms/mlx_lm/server.py

@@ -140,7 +140,8 @@ class APIHandler(BaseHTTPRequestHandler):
         self.validate_model_parameters()
 
         # Get stop id sequences, if provided
-        stop_words = self.body.get("stop", [])
+        stop_words = self.body.get("stop")
+        stop_words = stop_words or []
         stop_words = [stop_words] if isinstance(stop_words, str) else stop_words
         stop_id_sequences = [
             self.tokenizer.encode(stop_word, add_special_tokens=False)
@@ -171,14 +172,14 @@ class APIHandler(BaseHTTPRequestHandler):
         if not isinstance(self.max_tokens, int) or self.max_tokens < 0:
             raise ValueError("max_tokens must be a non-negative integer")
 
-        if not isinstance(self.temperature, float) or self.temperature < 0:
+        if not isinstance(self.temperature, (float, int)) or self.temperature < 0:
             raise ValueError("temperature must be a non-negative float")
 
-        if not isinstance(self.top_p, float) or self.top_p < 0 or self.top_p > 1:
+        if not isinstance(self.top_p, (float, int)) or self.top_p < 0 or self.top_p > 1:
             raise ValueError("top_p must be a float between 0 and 1")
 
         if (
-            not isinstance(self.repetition_penalty, float)
+            not isinstance(self.repetition_penalty, (float, int))
             or self.repetition_penalty < 0
         ):
             raise ValueError("repetition_penalty must be a non-negative float")
@@ -527,6 +528,18 @@ def main():
         help="Set the MLX cache limit in GB",
         required=False,
     )
+    parser.add_argument(
+        "--chat-template",
+        type=str,
+        default="",
+        help="Specify a chat template for the tokenizer",
+        required=False,
+    )
+    parser.add_argument(
+        "--use-default-chat-template",
+        action="store_true",
+        help="Use the default chat template",
+    )
     args = parser.parse_args()
 
     logging.basicConfig(
@@ -540,10 +553,17 @@ def main():
 
     # Building tokenizer_config
     tokenizer_config = {"trust_remote_code": True if args.trust_remote_code else None}
+    if args.chat_template:
+        tokenizer_config["chat_template"] = args.chat_template
 
     model, tokenizer = load(
         args.model, adapter_path=args.adapter_path, tokenizer_config=tokenizer_config
     )
+
+    if args.use_default_chat_template:
+        if tokenizer.chat_template is None:
+            tokenizer.chat_template = tokenizer.default_chat_template
+
     run(args.host, args.port, model, tokenizer)