Add **kwargs to model base class constructors (#9252)

Updated constructors for base and derived classes in chat, embedding,
rerank, sequence2txt, and tts models to accept **kwargs. This change
improves extensibility and allows passing additional parameters without
breaking existing interfaces.

- [x] Bug Fix (non-breaking change which fixes an issue)

---------

Co-authored-by: IT: Sop.Son <sop.son@feavn.local>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

rag/llm/sequence2txt_model.py

@@ -28,7 +28,11 @@ from rag.utils import num_tokens_from_string
 
 
 class Base(ABC):
-    def __init__(self, key, model_name):
+    def __init__(self, key, model_name, **kwargs):
+        """
+        Abstract base class constructor.
+        Parameters are not stored; initialization is left to subclasses.
+        """
         pass
 
     def transcription(self, audio, **kwargs):