Fix batches api cost tracking + Log batch models in spend logs / standard logging payload (#9077)

* feat(batches/): fix batch cost calculation - ensure it's accurate

use the correct cost value - prev. defaulting to non-batch cost

* feat(batch_utils.py): log batch models to spend logs + standard logging payload

makes it easy to understand how cost was calculated

* fix: fix stored payload for test

* test: fix test

litellm/proxy/spend_tracking/spend_tracking_utils.py

@@ -35,7 +35,9 @@ def _is_master_key(api_key: str, _master_key: Optional[str]) -> bool:
 
 
 def _get_spend_logs_metadata(
-    metadata: Optional[dict], applied_guardrails: Optional[List[str]] = None
+    metadata: Optional[dict],
+    applied_guardrails: Optional[List[str]] = None,
+    batch_models: Optional[List[str]] = None,
 ) -> SpendLogsMetadata:
     if metadata is None:
         return SpendLogsMetadata(
@@ -52,6 +54,7 @@ def _get_spend_logs_metadata(
             status=None or "success",
             error_information=None,
             proxy_server_request=None,
+            batch_models=None,
         )
     verbose_proxy_logger.debug(
         "getting payload for SpendLogs, available keys in metadata: "
@@ -67,7 +70,7 @@ def _get_spend_logs_metadata(
         }
     )
     clean_metadata["applied_guardrails"] = applied_guardrails
-
+    clean_metadata["batch_models"] = batch_models
     return clean_metadata
 
 
@@ -192,6 +195,11 @@ def get_logging_payload(  # noqa: PLR0915
             if standard_logging_payload is not None
             else None
         ),
+        batch_models=(
+            standard_logging_payload.get("hidden_params", {}).get("batch_models", None)
+            if standard_logging_payload is not None
+            else None
+        ),
     )
 
     special_usage_fields = ["completion_tokens", "prompt_tokens", "total_tokens"]