Fix small bugs

Author: njbbaer

src/api_client.py

@@ -65,4 +65,4 @@ async def _fetch_details(self, generation_id: str) -> dict[str, Any]:
                     return response.json()
                 except httpx.HTTPError:
                     await asyncio.sleep(0.5)
-            return {"data": {"total_cost": 0.0, "cache_discount": 0.0}}
+            return {"data": {"upstream_inference_cost": 0.0, "cache_discount": 0.0}}

src/chat_completion.py

@@ -20,7 +20,7 @@ def completion_tokens(self) -> int:
 
     @property
     def cache_discount_string(self) -> str:
-        if not self._cache_discount:
+        if self._cache_discount is None:
             return "N/A"
 
         sign = "-" if self._cache_discount < 0 else ""