Guard against non-dict JSON messages in the receive loop

json.loads can return lists, strings, numbers, or null. These
would crash _handle_message which expects a dict. Now emits an
error event and continues instead.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: PaulAsjes

src/elevenlabs/speech_engine/session.py

@@ -253,6 +253,13 @@ async def run(self) -> None:
                     await self._emit("error", e)
                     continue
 
+                if not isinstance(msg, dict):
+                    await self._emit(
+                        "error",
+                        ValueError(f"expected JSON object, got {type(msg).__name__}"),
+                    )
+                    continue
+
                 await self._handle_message(msg)
         except asyncio.CancelledError:
             raise