Model: Prompt users to install extras if dependencies don't exist

Ex: tokenizers, lmfe, outlines.

Signed-off-by: kingbri <bdashore3@proton.me>

backends/exllamav2/model.py

@@ -399,7 +399,19 @@ class ExllamaV2Container:
         ExLlamaV2Tokenizer.extended_id_to_piece = {}
         ExLlamaV2Tokenizer.extended_piece_to_id = {}
 
-        self.tokenizer = ExLlamaV2Tokenizer(self.config)
+        try:
+            self.tokenizer = ExLlamaV2Tokenizer(self.config)
+        except AssertionError as exc:
+            if "HF tokenizer" in str(exc):
+                raise ImportError(
+                    "Could not create ExllamaV2's tokenizer for this model "
+                    "because tokenizers is not installed.\n"
+                    "Please run the following command in your environment "
+                    "to install extra packages:\n"
+                    "pip install -U .[extras]"
+                ) from exc
+            else:
+                raise exc
 
         # Calculate autosplit reserve for all GPUs
         gpu_count = torch.cuda.device_count()