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/litellm_core_utils/litellm_logging.py

@@ -1613,11 +1613,12 @@ class Logging(LiteLLMLoggingBaseClass):
             result, LiteLLMBatch
         ):
 
-            response_cost, batch_usage = await _handle_completed_batch(
+            response_cost, batch_usage, batch_models = await _handle_completed_batch(
                 batch=result, custom_llm_provider=self.custom_llm_provider
             )
 
             result._hidden_params["response_cost"] = response_cost
+            result._hidden_params["batch_models"] = batch_models
             result.usage = batch_usage
 
         start_time, end_time, result = self._success_handler_helper_fn(
@@ -3213,6 +3214,7 @@ class StandardLoggingPayloadSetup:
             response_cost=None,
             additional_headers=None,
             litellm_overhead_time_ms=None,
+            batch_models=None,
         )
         if hidden_params is not None:
             for key in StandardLoggingHiddenParams.__annotations__.keys():
@@ -3326,6 +3328,7 @@ def get_standard_logging_object_payload(
                         api_base=None,
                         response_cost=None,
                         litellm_overhead_time_ms=None,
+                        batch_models=None,
                     )
                 )
 
@@ -3610,6 +3613,7 @@ def create_dummy_standard_logging_payload() -> StandardLoggingPayload:
         response_cost=None,
         additional_headers=None,
         litellm_overhead_time_ms=None,
+        batch_models=None,
     )
 
     # Convert numeric values to appropriate types