fix: Fix invalid cache_creation_tokens metric key (#195)

Author: corona10

src/api/models/bedrock.py

@@ -375,7 +375,7 @@ async def chat(self, chat_request: ChatRequest) -> ChatResponse:
 
         # Extract prompt caching metrics if available
         cache_read_tokens = usage.get("cacheReadInputTokens", 0)
-        cache_creation_tokens = usage.get("cacheCreationInputTokens", 0)
+        cache_creation_tokens = usage.get("cacheWriteInputTokens", 0)
 
         # Calculate actual prompt tokens
         # Bedrock's totalTokens includes all: inputTokens + cacheRead + cacheWrite + outputTokens
@@ -1035,7 +1035,7 @@ def _create_response_stream(
 
                 # Extract prompt caching metrics if available
                 cache_read_tokens = usage_data.get("cacheReadInputTokens", 0)
-                cache_creation_tokens = usage_data.get("cacheCreationInputTokens", 0)
+                cache_creation_tokens = usage_data.get("cacheWriteInputTokens", 0)
 
                 # Create prompt_tokens_details if cache metrics are available
                 prompt_tokens_details = None