fix: conform AWSNovaSonicLLMService.get_setup_params to its protocol

The service implements the NovaSonicSessionSender protocol so the
session-continuation helper can target either the current or next
session. The protocol declares
`get_setup_params(self) -> tuple[str | None, list]`, but the
implementation was unannotated and could return NotGiven in the tools
position when from_standard_tools fell through to its NotGiven
sentinel. Add the matching return annotation and coerce the NotGiven
case to an empty list.

src/pipecat/services/aws/nova_sonic/llm.py

@@ -1106,7 +1106,7 @@ class AWSNovaSonicLLMService(LLMService):
         '''
         await self.send_event(event_json, stream)
 
-    def get_setup_params(self):
+    def get_setup_params(self) -> tuple[str | None, list]:
         """Return ``(system_instruction, tools)`` for the next session setup."""
         if not self._context:
             return None, []
@@ -1115,7 +1115,9 @@ class AWSNovaSonicLLMService(LLMService):
             self._context, system_instruction=self._settings.system_instruction
         )
         tools = (
-            llm_params["tools"] if llm_params["tools"] else adapter.from_standard_tools(self._tools)
+            llm_params["tools"]
+            if llm_params["tools"]
+            else (adapter.from_standard_tools(self._tools) or [])
         )
         return llm_params["system_instruction"], tools