Add documentation explaining __new__ usage in Nvidia class

Co-authored-by: VinciGit00 <[email protected]>

Author: Copilot

scrapegraphai/models/nvidia.py

@@ -8,6 +8,11 @@ class Nvidia:
     A wrapper for the ChatNVIDIA class that provides default configuration
     and could be extended with additional methods if needed.
 
+    Note: This class uses __new__ instead of __init__ because langchain_nvidia_ai_endpoints
+    is an optional dependency. We cannot inherit from ChatNVIDIA at class definition time
+    since the module may not be installed. The __new__ method allows us to lazily import
+    and return a ChatNVIDIA instance only when Nvidia() is instantiated.
+
     Args:
         llm_config (dict): Configuration parameters for the language model.
     """