refactor: drop dead _UNSET/None remap on temperature in legacy dispatch

The temperature default is now 0.0 so _UNSET is unreachable, and the
legacy leaf creators already skip the temperature kwarg when it's None
(see _legacy/chat_model_factory.py:54). Forwarding directly preserves
caller intent.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: cosminacho

src/uipath_langchain/chat/chat_model_factory.py

@@ -138,7 +138,7 @@ def _legacy_chat_model(
 
     return _legacy_get_chat_model(
         model,
-        temperature if temperature is not _UNSET and temperature is not None else 0.0,
+        temperature,
         max_tokens,
         agenthub_config,
         byo_connection_id,