server: fix streaming crashes (#13786)

* add preludes to content on partial regex match

* allow all parsers to parse non-tool-call content.

* tweak order of <|python_tag|> vs <function= parsing for functionary v3.1 format. still not ideal but hopefully less prone to crash

common/chat.h

@@ -144,6 +144,7 @@ struct common_chat_syntax {
     // Whether reasoning_content should be inlined in the content (e.g. for reasoning_format=deepseek in stream mode)
     bool                     reasoning_in_content  = false;
     bool                     thinking_forced_open  = false;
+    bool                     parse_tool_calls      = true;
 };
 
 // Check if the template supplied via "--chat-template" is supported or not. Returns true if it's valid