server : Add option to return token pieces in /tokenize endpoint (#9108)

* server : added with_pieces functionality to /tokenize endpoint

* server : Add tokenize with pieces tests to server.feature

* Handle case if tokenizer splits along utf8 continuation bytes

* Add example of token splitting

* Remove trailing ws

* Fix trailing ws

* Maybe fix ci

* maybe this fix windows ci?

---------

Co-authored-by: Xuan Son Nguyen <son@huggingface.co>

examples/server/tests/features/server.feature

@@ -105,6 +105,14 @@ Feature: llama.cpp server
     Given first token is removed
     Then  tokens can be detokenized
 
+  Scenario: Tokenize with pieces
+    When  tokenizing with pieces:
+    """
+    What is the capital of Germany?
+    媽
+    """
+    Then  tokens are given with pieces
+
   Scenario: Models available
     Given available models
     Then  1 models are supported